Merged changes from main branch

platforms/cpu/include/CpuCustomNonbondedForce.h

 
-/* Portions copyright (c) 2009-2016 Stanford University and Simbios.
+/* Portions copyright (c) 2009-2017 Stanford University and Simbios.
  * Contributors: Peter Eastman
  *
  * Permission is hereby granted, free of charge, to any person obtaining
@@ -122,7 +122,6 @@ class CpuCustomNonbondedForce {
                           double* fixedParameters, const std::map<std::string, double>& globalParameters,
                           std::vector<AlignedArray<float> >& threadForce, bool includeForce, bool includeEnergy, double& totalEnergy, double* energyParamDerivs);
 private:
-    class ComputeForceTask;
     class ThreadData;
 
     bool cutoff;

platforms/cpu/include/CpuGBSAOBCForce.h

 
-/* Portions copyright (c) 2006-2013 Stanford University and Simbios.
+/* Portions copyright (c) 2006-2017 Stanford University and Simbios.
  * Contributors: Pande Group
  *
  * Permission is hereby granted, free of charge, to any person obtaining
@@ -36,7 +36,6 @@ namespace OpenMM {
 
 class CpuGBSAOBCForce {
 public:
-    class ComputeTask;
     CpuGBSAOBCForce();
 
     /**

platforms/cpu/include/CpuGayBerneForce.h

@@ -6,7 +6,7 @@
  * Biological Structures at Stanford, funded under the NIH Roadmap for        *
  * Medical Research, grant U54 GM072970. See https://simtk.org.               *
  *                                                                            *
- * Portions copyright (c) 2016 Stanford University and the Authors.           *
+ * Portions copyright (c) 2016-2017 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -45,7 +45,6 @@ namespace OpenMM {
 class CpuGayBerneForce {
 public:
     struct Matrix;
-    class ComputeTask;
 
     /**
      * Constructor.

platforms/cpu/include/CpuKernels.h

@@ -54,8 +54,6 @@ namespace OpenMM {
  */
 class CpuCalcForcesAndEnergyKernel : public CalcForcesAndEnergyKernel {
 public:
-    class InitForceTask;
-    class SumForceTask;
     CpuCalcForcesAndEnergyKernel(std::string name, const Platform& platform, CpuPlatform::PlatformData& data, ContextImpl& context);
     /**
      * Initialize the kernel.
@@ -258,20 +256,30 @@ public:
      * @param nz      the number of grid points along the Z axis
      */
     void getPMEParameters(double& alpha, int& nx, int& ny, int& nz) const;
+    /**
+     * Get the parameters being used for the dispersion term in LJPME.
+     *
+     * @param alpha   the separation parameter
+     * @param nx      the number of grid points along the X axis
+     * @param ny      the number of grid points along the Y axis
+     * @param nz      the number of grid points along the Z axis
+     */
+    void getLJPMEParameters(double& alpha, int& nx, int& ny, int& nz) const;
 private:
     class PmeIO;
     CpuPlatform::PlatformData& data;
     int numParticles, num14;
     int **bonded14IndexArray;
     double **bonded14ParamArray;
-    double nonbondedCutoff, switchingDistance, rfDielectric, ewaldAlpha, ewaldSelfEnergy, dispersionCoefficient;
-    int kmax[3], gridSize[3];
-    bool useSwitchingFunction, useOptimizedPme, hasInitializedPme;
+    double nonbondedCutoff, switchingDistance, rfDielectric, ewaldAlpha, ewaldDispersionAlpha, ewaldSelfEnergy, dispersionCoefficient;
+    int kmax[3], gridSize[3], dispersionGridSize[3];
+    bool useSwitchingFunction, useOptimizedPme, hasInitializedPme, hasInitializedDispersionPme;
     std::vector<std::set<int> > exclusions;
     std::vector<std::pair<float, float> > particleParams;
+    std::vector<float> C6params;
     NonbondedMethod nonbondedMethod;
     CpuNonbondedForce* nonbonded;
-    Kernel optimizedPme;
+    Kernel optimizedPme, optimizedDispersionPme;
     CpuBondForce bondForce;
 };
 

platforms/cpu/include/CpuLangevinDynamics.h

 
-/* Portions copyright (c) 2013-2016 Stanford University and Simbios.
+/* Portions copyright (c) 2013-2017 Stanford University and Simbios.
  * Authors: Peter Eastman
  * Contributors: 
  *
@@ -35,9 +35,6 @@ namespace OpenMM {
 
 class CpuLangevinDynamics : public ReferenceStochasticDynamics {
 public:
-    class Update1Task;
-    class Update2Task;
-    class Update3Task;
     /**
      * Constructor.
      *

platforms/cpu/include/CpuNeighborList.h

@@ -9,7 +9,7 @@
  * Biological Structures at Stanford, funded under the NIH Roadmap for        *
  * Medical Research, grant U54 GM072970. See https://simtk.org.               *
  *                                                                            *
- * Portions copyright (c) 2013-2016 Stanford University and the Authors.      *
+ * Portions copyright (c) 2013-2017 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -45,7 +45,6 @@ namespace OpenMM {
 
 class OPENMM_EXPORT_CPU CpuNeighborList {
 public:
-    class ThreadTask;
     class Voxels;
     CpuNeighborList(int blockSize);
     void computeNeighborList(int numAtoms, const AlignedArray<float>& atomLocations, const std::vector<std::set<int> >& exclusions,

platforms/cpu/include/CpuNonbondedForce.h

 
-/* Portions copyright (c) 2006-2015 Stanford University and Simbios.
+/* Portions copyright (c) 2006-2017 Stanford University and Simbios.
  * Contributors: Pande Group
  *
  * Permission is hereby granted, free of charge, to any person obtaining
@@ -39,7 +39,6 @@ namespace OpenMM {
 
 class CpuNonbondedForce {
     public:
-        class ComputeDirectTask;
 
       /**---------------------------------------------------------------------------------------
       
@@ -114,6 +113,17 @@ class CpuNonbondedForce {
 
       void setUsePME(float alpha, int meshSize[3]);
 
+      /**---------------------------------------------------------------------------------------
+
+         Set the force to use Particle-Mesh Ewald (PME) summation for dispersion.
+
+         @param alpha    the Ewald separation parameter
+         @param gridSize the dimensions of the mesh
+
+         --------------------------------------------------------------------------------------- */
+
+      void setUseLJPME(float alpha, int meshSize[3]);
+
       /**---------------------------------------------------------------------------------------
       
          Calculate Ewald ixn
@@ -122,6 +132,7 @@ class CpuNonbondedForce {
          @param posq             atom coordinates and charges
          @param atomCoordinates  atom coordinates (in format needed by PME)
          @param atomParameters   atom parameters (sigma/2, 2*sqrt(epsilon))
+         @param C6Paramrs        C6 parameters for multiplicative representation of dispersion
          @param exclusions       atom exclusion indices
                                  exclusions[atomIndex] contains the list of exclusions for that atom
          @param forces           force array (forces added)
@@ -130,8 +141,8 @@ class CpuNonbondedForce {
          --------------------------------------------------------------------------------------- */
 
       void calculateReciprocalIxn(int numberOfAtoms, float* posq, const std::vector<Vec3>& atomCoordinates,
-                            const std::vector<std::pair<float, float> >& atomParameters, const std::vector<std::set<int> >& exclusions,
-                            std::vector<Vec3>& forces, double* totalEnergy) const;
+                                  const std::vector<std::pair<float, float> >& atomParameters, const std::vector<float> &C6params,
+                                  const std::vector<std::set<int> >& exclusions, std::vector<Vec3>& forces, double* totalEnergy) const;
       
       /**---------------------------------------------------------------------------------------
       
@@ -150,7 +161,7 @@ class CpuNonbondedForce {
          --------------------------------------------------------------------------------------- */
           
       void calculateDirectIxn(int numberOfAtoms, float* posq, const std::vector<Vec3>& atomCoordinates, const std::vector<std::pair<float, float> >& atomParameters,
-            const std::vector<std::set<int> >& exclusions, std::vector<AlignedArray<float> >& threadForce, double* totalEnergy, ThreadPool& threads);
+            const std::vector<float>& C6params, const std::vector<std::set<int> >& exclusions, std::vector<AlignedArray<float> >& threadForce, double* totalEnergy, ThreadPool& threads);
 
     /**
      * This routine contains the code executed by each thread.
@@ -163,28 +174,32 @@ protected:
         bool periodic;
         bool triclinic;
         bool ewald;
-        bool pme;
-        bool tableIsValid;
+        bool ljpme, pme;
+        bool tableIsValid, expTableIsValid;
         const CpuNeighborList* neighborList;
         float recipBoxSize[3];
         Vec3 periodicBoxVectors[3];
         AlignedArray<fvec4> periodicBoxVec4;
         float cutoffDistance, switchingDistance;
         float krf, crf;
-        float alphaEwald;
+        float alphaEwald, alphaDispersionEwald;
         int numRx, numRy, numRz;
-        int meshDim[3];
+        int meshDim[3], dispersionMeshDim[3];
         std::vector<float> erfcTable, ewaldScaleTable;
-        float ewaldDX, ewaldDXInv, erfcDXInv;
+        std::vector<float> exptermsTable, dExptermsTable;
+        float ewaldDX, ewaldDXInv, erfcDXInv, exptermsDX, exptermsDXInv;
         std::vector<double> threadEnergy;
         // The following variables are used to make information accessible to the individual threads.
         int numberOfAtoms;
         float* posq;
         Vec3 const* atomCoordinates;
         std::pair<float, float> const* atomParameters;        
+        float const *C6params;
         std::set<int> const* exclusions;
         std::vector<AlignedArray<float> >* threadForce;
         bool includeEnergy;
+        float inverseRcut6;
+        float inverseRcut6Expterm;
         void* atomicCounter;
 
         static const float TWO_OVER_SQRT_PI;
@@ -238,10 +253,29 @@ protected:
        */
       void tabulateEwaldScaleFactor();
 
+      /**
+       * Create a lookup table for the scale factor used with dispersion PME.
+       */
+      void tabulateExpTerms();
+
       /**
        * Compute a fast approximation to erfc(x).
        */
       float erfcApprox(float x);
+
+      /**
+       * Compute a fast approximation to (1.0 - EXP(-dar^2) * (1.0 + dar^2 + 0.5*dar^4))
+       * where dar = (dispersionAlpha * R)
+       * needed for LJPME energies.
+       */
+      float exptermsApprox(float R);
+
+      /**
+       * Compute a fast approximation to (1.0 - EXP(-dar^2) * (1.0 + dar^2 + 0.5*dar^4 + dar^6/6.0))
+       * where dar = (dispersionAlpha * R)
+       * needed for LJPME forces.
+       */
+      float dExptermsApprox(float R);
 };
 
 } // namespace OpenMM

platforms/cpu/include/CpuNonbondedForceVec4.h

@@ -93,6 +93,20 @@ protected:
        * Evaluate the scale factor used with Ewald and PME: erfc(alpha*r) + 2*alpha*r*exp(-alpha*alpha*r*r)/sqrt(PI)
        */
       fvec4 ewaldScaleFunction(const fvec4& x);
+
+      /**
+       * Compute a fast approximation to (1.0 - EXP(-dar^2) * (1.0 + dar^2 + 0.5*dar^4))
+       * where dar = (dispersionAlpha * R)
+       * needed for LJPME energies.
+       */
+      fvec4 exptermsApprox(const fvec4& R);
+
+      /**
+       * Compute a fast approximation to (1.0 - EXP(-dar^2) * (1.0 + dar^2 + 0.5*dar^4 + dar^6/6.0))
+       * where dar = (dispersionAlpha * R)
+       * needed for LJPME forces.
+       */
+      fvec4 dExptermsApprox(const fvec4& R);
 };
 
 } // namespace OpenMM

platforms/cpu/include/CpuNonbondedForceVec8.h

@@ -92,6 +92,21 @@ protected:
        * Evaluate the scale factor used with Ewald and PME: erfc(alpha*r) + 2*alpha*r*exp(-alpha*alpha*r*r)/sqrt(PI)
        */
       fvec8 ewaldScaleFunction(const fvec8& x);
+
+      /**
+       * Compute a fast approximation to (1.0 - EXP(-dar^2) * (1.0 + dar^2 + 0.5*dar^4))
+       * where dar = (dispersionAlpha * R)
+       * needed for LJPME energies.
+       */
+      fvec8 exptermsApprox(const fvec8& R);
+
+      /**
+       * Compute a fast approximation to (1.0 - EXP(-dar^2) * (1.0 + dar^2 + 0.5*dar^4 + dar^6/6.0))
+       * where dar = (dispersionAlpha * R)
+       * needed for LJPME forces.
+       */
+      fvec8 dExptermsApprox(const fvec8& R);
+
 };
 
 } // namespace OpenMM

platforms/cpu/include/CpuSETTLE.h

@@ -9,7 +9,7 @@
  * Biological Structures at Stanford, funded under the NIH Roadmap for        *
  * Medical Research, grant U54 GM072970. See https://simtk.org.               *
  *                                                                            *
- * Portions copyright (c) 2013 Stanford University and the Authors.           *
+ * Portions copyright (c) 2013-2017 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -45,8 +45,6 @@ namespace OpenMM {
  */
 class OPENMM_EXPORT_CPU CpuSETTLE : public ReferenceConstraintAlgorithm {
 public:
-    class ApplyToPositionsTask;
-    class ApplyToVelocitiesTask;
     CpuSETTLE(const System& system, const ReferenceSETTLEAlgorithm& settle, ThreadPool& threads);
     ~CpuSETTLE();
 

platforms/cpu/src/CpuBondForce.cpp

@@ -6,7 +6,7 @@
  * Biological Structures at Stanford, funded under the NIH Roadmap for        *
  * Medical Research, grant U54 GM072970. See https://simtk.org.               *
  *                                                                            *
- * Portions copyright (c) 2014-2016 Stanford University and the Authors.      *
+ * Portions copyright (c) 2014-2017 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -35,25 +35,6 @@
 using namespace OpenMM;
 using namespace std;
 
-class CpuBondForce::ComputeForceTask : public ThreadPool::Task {
-public:
-    ComputeForceTask(CpuBondForce& owner, vector<Vec3>& atomCoordinates, double** parameters, vector<Vec3>& forces, 
-        vector<double>& threadEnergy, double* totalEnergy, ReferenceBondIxn& referenceBondIxn) : owner(owner), atomCoordinates(atomCoordinates),
-        parameters(parameters), forces(forces), threadEnergy(threadEnergy), totalEnergy(totalEnergy), referenceBondIxn(referenceBondIxn) {
-    }
-    void execute(ThreadPool& threads, int threadIndex) {
-        double* energy = (totalEnergy == NULL ? NULL : &threadEnergy[threadIndex]);
-        owner.threadComputeForce(threads, threadIndex, atomCoordinates, parameters, forces, energy, referenceBondIxn);
-    }
-    CpuBondForce& owner;
-    vector<Vec3>& atomCoordinates;
-    double** parameters;
-    vector<Vec3>& forces;
-    vector<double>& threadEnergy;
-    double* totalEnergy;
-    ReferenceBondIxn& referenceBondIxn;
-};
-
 CpuBondForce::CpuBondForce() {
 }
 
@@ -188,8 +169,10 @@ void CpuBondForce::calculateForce(vector<Vec3>& atomCoordinates, double** parame
     // Have the worker threads compute their forces.
     
     vector<double> threadEnergy(threads->getNumThreads(), 0);
-    ComputeForceTask task(*this, atomCoordinates, parameters, forces, threadEnergy, totalEnergy, referenceBondIxn);
-    threads->execute(task);
+    threads->execute([&] (ThreadPool& threads, int threadIndex) {
+        double* energy = (totalEnergy == NULL ? NULL : &threadEnergy[threadIndex]);
+        threadComputeForce(threads, threadIndex, atomCoordinates, parameters, forces, energy, referenceBondIxn);
+    });
     threads->waitForThreads();
     
     // Compute any "extra" bonds.

platforms/cpu/src/CpuCustomGBForce.cpp

 
-/* Portions copyright (c) 2009-2016 Stanford University and Simbios.
+/* Portions copyright (c) 2009-2017 Stanford University and Simbios.
  * Contributors: Peter Eastman
  *
  * Permission is hereby granted, free of charge, to any person obtaining
@@ -33,16 +33,6 @@
 using namespace OpenMM;
 using namespace std;
 
-class CpuCustomGBForce::ComputeForceTask : public ThreadPool::Task {
-public:
-    ComputeForceTask(CpuCustomGBForce& owner) : owner(owner) {
-    }
-    void execute(ThreadPool& threads, int threadIndex) {
-        owner.threadComputeForce(threads, threadIndex);
-    }
-    CpuCustomGBForce& owner;
-};
-
 CpuCustomGBForce::ThreadData::ThreadData(int numAtoms, int numThreads, int threadIndex,
                       const vector<Lepton::CompiledExpression>& valueExpressions,
                       const vector<vector<Lepton::CompiledExpression> >& valueDerivExpressions,
@@ -206,7 +196,7 @@ void CpuCustomGBForce::calculateIxn(int numberOfAtoms, float* posq, double** ato
 
     // Calculate the first computed value.
 
-    ComputeForceTask task(*this);
+    auto task = [&] (ThreadPool& threads, int threadIndex) { threadComputeForce(threads, threadIndex); };
     gmx_atomic_set(&counter, 0);
     threads.execute(task);
     threads.waitForThreads();

platforms/cpu/src/CpuCustomManyParticleForce.cpp

 
-/* Portions copyright (c) 2009-2014 Stanford University and Simbios.
+/* Portions copyright (c) 2009-2017 Stanford University and Simbios.
  * Contributors: Peter Eastman
  *
  * Permission is hereby granted, free of charge, to any person obtaining
@@ -37,16 +37,6 @@
 using namespace OpenMM;
 using namespace std;
 
-class CpuCustomManyParticleForce::ComputeForceTask : public ThreadPool::Task {
-public:
-    ComputeForceTask(CpuCustomManyParticleForce& owner) : owner(owner) {
-    }
-    void execute(ThreadPool& threads, int threadIndex) {
-        owner.threadComputeForce(threads, threadIndex);
-    }
-    CpuCustomManyParticleForce& owner;
-};
-
 CpuCustomManyParticleForce::CpuCustomManyParticleForce(const CustomManyParticleForce& force, ThreadPool& threads) :
             threads(threads), useCutoff(false), usePeriodic(false), neighborList(NULL) {
     numParticles = force.getNumParticles();
@@ -141,8 +131,7 @@ void CpuCustomManyParticleForce::calculateIxn(AlignedArray<float>& posq, double*
     
     // Signal the threads to start running and wait for them to finish.
     
-    ComputeForceTask task(*this);
-    threads.execute(task);
+    threads.execute([&] (ThreadPool& threads, int threadIndex) { threadComputeForce(threads, threadIndex); });
     threads.waitForThreads();
     
     // Combine the energies from all the threads.

platforms/cpu/src/CpuCustomNonbondedForce.cpp

 
-/* Portions copyright (c) 2009-2016 Stanford University and Simbios.
+/* Portions copyright (c) 2009-2017 Stanford University and Simbios.
  * Contributors: Peter Eastman
  *
  * Permission is hereby granted, free of charge, to any person obtaining
@@ -33,16 +33,6 @@
 using namespace OpenMM;
 using namespace std;
 
-class CpuCustomNonbondedForce::ComputeForceTask : public ThreadPool::Task {
-public:
-    ComputeForceTask(CpuCustomNonbondedForce& owner) : owner(owner) {
-    }
-    void execute(ThreadPool& threads, int threadIndex) {
-        owner.threadComputeForce(threads, threadIndex);
-    }
-    CpuCustomNonbondedForce& owner;
-};
-
 CpuCustomNonbondedForce::ThreadData::ThreadData(const Lepton::CompiledExpression& energyExpression, const Lepton::CompiledExpression& forceExpression,
             const vector<string>& parameterNames, const std::vector<Lepton::CompiledExpression> energyParamDerivExpressions) :
             energyExpression(energyExpression), forceExpression(forceExpression), energyParamDerivExpressions(energyParamDerivExpressions) {
@@ -150,8 +140,7 @@ void CpuCustomNonbondedForce::calculatePairIxn(int numberOfAtoms, float* posq, v
     
     // Signal the threads to start running and wait for them to finish.
     
-    ComputeForceTask task(*this);
-    threads.execute(task);
+    threads.execute([&] (ThreadPool& threads, int threadIndex) { threadComputeForce(threads, threadIndex); });
     threads.waitForThreads();
     
     // Combine the energies from all the threads.

platforms/cpu/src/CpuGBSAOBCForce.cpp

-/* Portions copyright (c) 2006-2016 Stanford University and Simbios.
+/* Portions copyright (c) 2006-2017 Stanford University and Simbios.
  * Contributors: Pande Group
  *
  * Permission is hereby granted, free of charge, to any person obtaining
@@ -36,16 +36,6 @@ const int CpuGBSAOBCForce::NUM_TABLE_POINTS = 4096;
 const float CpuGBSAOBCForce::TABLE_MIN = 0.25f;
 const float CpuGBSAOBCForce::TABLE_MAX = 1.5f;
 
-class CpuGBSAOBCForce::ComputeTask : public ThreadPool::Task {
-public:
-    ComputeTask(CpuGBSAOBCForce& owner) : owner(owner) {
-    }
-    void execute(ThreadPool& threads, int threadIndex) {
-        owner.threadComputeForce(threads, threadIndex);
-    }
-    CpuGBSAOBCForce& owner;
-};
-
 CpuGBSAOBCForce::CpuGBSAOBCForce() : cutoff(false), periodic(false) {
     logDX = (TABLE_MAX-TABLE_MIN)/NUM_TABLE_POINTS;
     logDXInv = 1.0f/logDX;
@@ -110,9 +100,8 @@ void CpuGBSAOBCForce::computeForce(const AlignedArray<float>& posq, vector<Align
     
     // Signal the threads to start running and wait for them to finish.
     
-    ComputeTask task(*this);
     gmx_atomic_set(&counter, 0);
-    threads.execute(task);
+    threads.execute([&] (ThreadPool& threads, int threadIndex) { threadComputeForce(threads, threadIndex); });
     threads.waitForThreads(); // Compute Born radii
     gmx_atomic_set(&counter, 0);
     threads.resumeThreads();

platforms/cpu/src/CpuGayBerneForce.cpp

@@ -6,7 +6,7 @@
  * Biological Structures at Stanford, funded under the NIH Roadmap for        *
  * Medical Research, grant U54 GM072970. See https://simtk.org.               *
  *                                                                            *
- * Portions copyright (c) 2016 Stanford University and the Authors.           *
+ * Portions copyright (c) 2016-2017 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -44,17 +44,6 @@
 using namespace OpenMM;
 using namespace std;
 
-class CpuGayBerneForce::ComputeTask : public ThreadPool::Task {
-public:
-    ComputeTask(CpuGayBerneForce& owner, CpuNeighborList* neighborList) : owner(owner), neighborList(neighborList) {
-    }
-    void execute(ThreadPool& threads, int threadIndex) {
-        owner.threadComputeForce(threads, threadIndex, neighborList);
-    }
-    CpuGayBerneForce& owner;
-    CpuNeighborList* neighborList;
-};
-
 CpuGayBerneForce::CpuGayBerneForce(const GayBerneForce& force) {
     // Record the force parameters.
 
@@ -137,8 +126,7 @@ double CpuGayBerneForce::calculateForce(const vector<Vec3>& positions, std::vect
     
     // Signal the threads to compute the pairwise interactions.
     
-    ComputeTask task(*this, data.neighborList);
-    threads.execute(task);
+    threads.execute([&] (ThreadPool& threads, int threadIndex) { threadComputeForce(threads, threadIndex, data.neighborList); });
     threads.waitForThreads();
     
     // Signal the threads to compute exceptions.

platforms/cpu/src/CpuKernels.cpp

@@ -50,6 +50,7 @@
 #include "lepton/CustomFunction.h"
 #include "lepton/Operation.h"
 #include "lepton/Parser.h"
+#include <iostream>
 #include "lepton/ParsedExpression.h"
 
 using namespace OpenMM;
@@ -137,35 +138,27 @@ static double computeShiftedKineticEnergy(ContextImpl& context, vector<double>&
     return 0.5*energy;
 }
 
-class CpuCalcForcesAndEnergyKernel::SumForceTask : public ThreadPool::Task {
-public:
-    SumForceTask(int numParticles, vector<Vec3>& forceData, CpuPlatform::PlatformData& data) : numParticles(numParticles), forceData(forceData), data(data) {
-    }
-    void execute(ThreadPool& threads, int threadIndex) {
-        // Sum the contributions to forces that have been calculated by different threads.
+CpuCalcForcesAndEnergyKernel::CpuCalcForcesAndEnergyKernel(std::string name, const Platform& platform, CpuPlatform::PlatformData& data, ContextImpl& context) :
+        CalcForcesAndEnergyKernel(name, platform), data(data) {
+    // Create a Reference platform version of this kernel.
     
-        int numThreads = threads.getNumThreads();
-        int start = threadIndex*numParticles/numThreads;
-        int end = (threadIndex+1)*numParticles/numThreads;
-        for (int i = start; i < end; i++) {
-            fvec4 f(0.0f);
-            for (int j = 0; j < numThreads; j++)
-                f += fvec4(&data.threadForce[j][4*i]);
-            forceData[i][0] += f[0];
-            forceData[i][1] += f[1];
-            forceData[i][2] += f[2];
-        }
-    }
-    int numParticles;
-    vector<Vec3>& forceData;
-    CpuPlatform::PlatformData& data;
-};
+    ReferenceKernelFactory referenceFactory;
+    referenceKernel = Kernel(referenceFactory.createKernelImpl(name, platform, context));
+}
 
-class CpuCalcForcesAndEnergyKernel::InitForceTask : public ThreadPool::Task {
-public:
-    InitForceTask(int numParticles, ContextImpl& context, CpuPlatform::PlatformData& data) : numParticles(numParticles), positionsValid(true), context(context), data(data) {
-    }
-    void execute(ThreadPool& threads, int threadIndex) {
+void CpuCalcForcesAndEnergyKernel::initialize(const System& system) {
+    referenceKernel.getAs<ReferenceCalcForcesAndEnergyKernel>().initialize(system);
+    lastPositions.resize(system.getNumParticles(), Vec3(1e10, 1e10, 1e10));
+}
+
+void CpuCalcForcesAndEnergyKernel::beginComputation(ContextImpl& context, bool includeForce, bool includeEnergy, int groups) {
+    referenceKernel.getAs<ReferenceCalcForcesAndEnergyKernel>().beginComputation(context, includeForce, includeEnergy, groups);
+    
+    // Convert positions to single precision and clear the forces.
+
+    int numParticles = context.getSystem().getNumParticles();
+    bool positionsValid = true;
+    data.threads.execute([&] (ThreadPool& threads, int threadIndex) {
         // Convert the positions to single precision and apply periodic boundary conditions
 
         AlignedArray<float>& posq = data.posq;
@@ -218,36 +211,9 @@ public:
         fvec4 zero(0.0f);
         for (int j = 0; j < numParticles; j++)
             zero.store(&data.threadForce[threadIndex][j*4]);
-    }
-    int numParticles;
-    bool positionsValid;
-    ContextImpl& context;
-    CpuPlatform::PlatformData& data;
-};
-
-CpuCalcForcesAndEnergyKernel::CpuCalcForcesAndEnergyKernel(std::string name, const Platform& platform, CpuPlatform::PlatformData& data, ContextImpl& context) :
-        CalcForcesAndEnergyKernel(name, platform), data(data) {
-    // Create a Reference platform version of this kernel.
-    
-    ReferenceKernelFactory referenceFactory;
-    referenceKernel = Kernel(referenceFactory.createKernelImpl(name, platform, context));
-}
-
-void CpuCalcForcesAndEnergyKernel::initialize(const System& system) {
-    referenceKernel.getAs<ReferenceCalcForcesAndEnergyKernel>().initialize(system);
-    lastPositions.resize(system.getNumParticles(), Vec3(1e10, 1e10, 1e10));
-}
-
-void CpuCalcForcesAndEnergyKernel::beginComputation(ContextImpl& context, bool includeForce, bool includeEnergy, int groups) {
-    referenceKernel.getAs<ReferenceCalcForcesAndEnergyKernel>().beginComputation(context, includeForce, includeEnergy, groups);
-    
-    // Convert positions to single precision and clear the forces.
-
-    int numParticles = context.getSystem().getNumParticles();
-    InitForceTask task(numParticles, context, data);
-    data.threads.execute(task);
+    });
     data.threads.waitForThreads();
-    if (!task.positionsValid)
+    if (!positionsValid)
         throw OpenMMException("Particle coordinate is nan");
 
     // Determine whether we need to recompute the neighbor list.
@@ -302,8 +268,23 @@ void CpuCalcForcesAndEnergyKernel::beginComputation(ContextImpl& context, bool i
 double CpuCalcForcesAndEnergyKernel::finishComputation(ContextImpl& context, bool includeForce, bool includeEnergy, int groups, bool& valid) {
     // Sum the forces from all the threads.
     
-    SumForceTask task(context.getSystem().getNumParticles(), extractForces(context), data);
-    data.threads.execute(task);
+    data.threads.execute([&] (ThreadPool& threads, int threadIndex) {
+        // Sum the contributions to forces that have been calculated by different threads.
+        
+        int numParticles = context.getSystem().getNumParticles();
+        int numThreads = threads.getNumThreads();
+        int start = threadIndex*numParticles/numThreads;
+        int end = (threadIndex+1)*numParticles/numThreads;
+        vector<Vec3>& forceData = extractForces(context);
+        for (int i = start; i < end; i++) {
+            fvec4 f(0.0f);
+            for (int j = 0; j < numThreads; j++)
+                f += fvec4(&data.threadForce[j][4*i]);
+            forceData[i][0] += f[0];
+            forceData[i][1] += f[1];
+            forceData[i][2] += f[2];
+        }
+    });
     data.threads.waitForThreads();
     return referenceKernel.getAs<ReferenceCalcForcesAndEnergyKernel>().finishComputation(context, includeForce, includeEnergy, groups, valid);
 }
@@ -528,7 +509,7 @@ CpuNonbondedForce* createCpuNonbondedForceVec4();
 CpuNonbondedForce* createCpuNonbondedForceVec8();
 
 CpuCalcNonbondedForceKernel::CpuCalcNonbondedForceKernel(string name, const Platform& platform, CpuPlatform::PlatformData& data) : CalcNonbondedForceKernel(name, platform),
-        data(data), bonded14IndexArray(NULL), bonded14ParamArray(NULL), hasInitializedPme(false), nonbonded(NULL) {
+        data(data), bonded14IndexArray(NULL), bonded14ParamArray(NULL), hasInitializedPme(false), hasInitializedDispersionPme(false), nonbonded(NULL) {
     if (isVec8Supported())
         nonbonded = createCpuNonbondedForceVec8();
     else
@@ -575,12 +556,14 @@ void CpuCalcNonbondedForceKernel::initialize(const System& system, const Nonbond
     for (int i = 0; i < num14; i++)
         bonded14ParamArray[i] = new double[3];
     particleParams.resize(numParticles);
+    C6params.resize(numParticles);
     double sumSquaredCharges = 0.0;
     for (int i = 0; i < numParticles; ++i) {
         double charge, radius, depth;
         force.getParticleParameters(i, charge, radius, depth);
         data.posq[4*i+3] = (float) charge;
         particleParams[i] = make_pair((float) (0.5*radius), (float) (2.0*sqrt(depth)));
+        C6params[i] = 8.0*pow(particleParams[i].first, 3.0) * particleParams[i].second;
         sumSquaredCharges += charge*charge;
     }
     
@@ -616,19 +599,35 @@ void CpuCalcNonbondedForceKernel::initialize(const System& system, const Nonbond
     }
     else if (nonbondedMethod == PME) {
         double alpha;
-        NonbondedForceImpl::calcPMEParameters(system, force, alpha, gridSize[0], gridSize[1], gridSize[2]);
+        NonbondedForceImpl::calcPMEParameters(system, force, alpha, gridSize[0], gridSize[1], gridSize[2], false);
         ewaldAlpha = alpha;
     }
-    if (nonbondedMethod == Ewald || nonbondedMethod == PME)
+    else if (nonbondedMethod == LJPME) {
+        double alpha;
+        NonbondedForceImpl::calcPMEParameters(system, force, alpha, gridSize[0], gridSize[1], gridSize[2], false);
+        ewaldAlpha = alpha;
+        NonbondedForceImpl::calcPMEParameters(system, force, alpha, dispersionGridSize[0], dispersionGridSize[1], dispersionGridSize[2], true);
+        ewaldDispersionAlpha = alpha;
+        useSwitchingFunction = false;
+    }
+
+    if (nonbondedMethod == Ewald || nonbondedMethod == PME || nonbondedMethod == LJPME) {
         ewaldSelfEnergy = -ONE_4PI_EPS0*ewaldAlpha*sumSquaredCharges/sqrt(M_PI);
-    else
+        if(nonbondedMethod == LJPME){
+            for (int atom = 0; atom < numParticles; atom++) {
+                // Dispersion self term
+                ewaldSelfEnergy += pow(ewaldDispersionAlpha, 6.0) * C6params[atom]*C6params[atom] / 12.0;
+            }
+        }
+    } else {
         ewaldSelfEnergy = 0.0;
+    }
     rfDielectric = force.getReactionFieldDielectric();
     if (force.getUseDispersionCorrection())
         dispersionCoefficient = NonbondedForceImpl::calcDispersionCorrection(system, force);
     else
         dispersionCoefficient = 0.0;
-    data.isPeriodic = (nonbondedMethod == CutoffPeriodic || nonbondedMethod == Ewald || nonbondedMethod == PME);
+    data.isPeriodic = (nonbondedMethod == CutoffPeriodic || nonbondedMethod == Ewald || nonbondedMethod == PME || nonbondedMethod == LJPME);
 }
 
 double CpuCalcNonbondedForceKernel::execute(ContextImpl& context, bool includeForces, bool includeEnergy, bool includeDirect, bool includeReciprocal) {
@@ -646,6 +645,20 @@ double CpuCalcNonbondedForceKernel::execute(ContextImpl& context, bool includeFo
                 optimizedPme.getAs<CalcPmeReciprocalForceKernel>().initialize(gridSize[0], gridSize[1], gridSize[2], numParticles, ewaldAlpha);
             }
         }
+        if (nonbondedMethod == LJPME) {
+            // If available, use the optimized PME implementation.
+
+            vector<string> kernelNames;
+            kernelNames.push_back("CalcPmeReciprocalForce");
+            useOptimizedPme = getPlatform().supportsKernels(kernelNames);
+            if (useOptimizedPme) {
+                optimizedPme = getPlatform().createKernel(CalcPmeReciprocalForceKernel::Name(), context);
+                optimizedPme.getAs<CalcPmeReciprocalForceKernel>().initialize(gridSize[0], gridSize[1], gridSize[2], numParticles, ewaldAlpha);
+                optimizedDispersionPme = getPlatform().createKernel(CalcDispersionPmeReciprocalForceKernel::Name(), context);
+                optimizedDispersionPme.getAs<CalcDispersionPmeReciprocalForceKernel>().initialize(dispersionGridSize[0], dispersionGridSize[1],
+                                                                                                  dispersionGridSize[2], numParticles, ewaldDispersionAlpha);
+            }
+        }
     }
     AlignedArray<float>& posq = data.posq;
     vector<Vec3>& posData = extractPositions(context);
@@ -654,6 +667,7 @@ double CpuCalcNonbondedForceKernel::execute(ContextImpl& context, bool includeFo
     double energy = (includeReciprocal ? ewaldSelfEnergy : 0.0);
     bool ewald  = (nonbondedMethod == Ewald);
     bool pme  = (nonbondedMethod == PME);
+    bool ljpme = (nonbondedMethod == LJPME);
     if (nonbondedMethod != NoCutoff)
         nonbonded->setUseCutoff(nonbondedCutoff, *data.neighborList, rfDielectric);
     if (data.isPeriodic) {
@@ -669,9 +683,13 @@ double CpuCalcNonbondedForceKernel::execute(ContextImpl& context, bool includeFo
         nonbonded->setUsePME(ewaldAlpha, gridSize);
     if (useSwitchingFunction)
         nonbonded->setUseSwitchingFunction(switchingDistance);
+    if (ljpme){
+        nonbonded->setUsePME(ewaldAlpha, gridSize);
+        nonbonded->setUseLJPME(ewaldDispersionAlpha, dispersionGridSize);
+    }
     double nonbondedEnergy = 0;
     if (includeDirect)
-        nonbonded->calculateDirectIxn(numParticles, &posq[0], posData, particleParams, exclusions, data.threadForce, includeEnergy ? &nonbondedEnergy : NULL, data.threads);
+        nonbonded->calculateDirectIxn(numParticles, &posq[0], posData, particleParams, C6params, exclusions, data.threadForce, includeEnergy ? &nonbondedEnergy : NULL, data.threads);
     if (includeReciprocal) {
         if (useOptimizedPme) {
             PmeIO io(&posq[0], &data.threadForce[0][0], numParticles);
@@ -680,13 +698,13 @@ double CpuCalcNonbondedForceKernel::execute(ContextImpl& context, bool includeFo
             nonbondedEnergy += optimizedPme.getAs<CalcPmeReciprocalForceKernel>().finishComputation(io);
         }
         else
-            nonbonded->calculateReciprocalIxn(numParticles, &posq[0], posData, particleParams, exclusions, forceData, includeEnergy ? &nonbondedEnergy : NULL);
+            nonbonded->calculateReciprocalIxn(numParticles, &posq[0], posData, particleParams, C6params, exclusions, forceData, includeEnergy ? &nonbondedEnergy : NULL);
     }
     energy += nonbondedEnergy;
     if (includeDirect) {
         ReferenceLJCoulomb14 nonbonded14;
         bondForce.calculateForce(posData, bonded14ParamArray, forceData, includeEnergy ? &energy : NULL, nonbonded14);
-        if (data.isPeriodic)
+        if (data.isPeriodic && nonbondedMethod != LJPME)
             energy += dispersionCoefficient/(boxVectors[0][0]*boxVectors[1][1]*boxVectors[2][2]);
     }
     return energy;
@@ -739,7 +757,7 @@ void CpuCalcNonbondedForceKernel::copyParametersToContext(ContextImpl& context,
 }
 
 void CpuCalcNonbondedForceKernel::getPMEParameters(double& alpha, int& nx, int& ny, int& nz) const {
-    if (nonbondedMethod != PME)
+    if (nonbondedMethod != PME && nonbondedMethod != LJPME)
         throw OpenMMException("getPMEParametersInContext: This Context is not using PME");
     if (useOptimizedPme)
         optimizedPme.getAs<const CalcPmeReciprocalForceKernel>().getPMEParameters(alpha, nx, ny, nz);
@@ -751,6 +769,19 @@ void CpuCalcNonbondedForceKernel::getPMEParameters(double& alpha, int& nx, int&
     }
 }
 
+void CpuCalcNonbondedForceKernel::getLJPMEParameters(double& alpha, int& nx, int& ny, int& nz) const {
+    if (nonbondedMethod != LJPME)
+        throw OpenMMException("getPMEParametersInContext: This Context is not using PME");
+    if (useOptimizedPme)
+        optimizedDispersionPme.getAs<const CalcPmeReciprocalForceKernel>().getPMEParameters(alpha, nx, ny, nz);
+    else {
+        alpha = ewaldDispersionAlpha;
+        nx = dispersionGridSize[0];
+        ny = dispersionGridSize[1];
+        nz = dispersionGridSize[2];
+    }
+}
+
 CpuCalcCustomNonbondedForceKernel::CpuCalcCustomNonbondedForceKernel(string name, const Platform& platform, CpuPlatform::PlatformData& data) :
             CalcCustomNonbondedForceKernel(name, platform), data(data), forceCopy(NULL), nonbonded(NULL) {
 }

platforms/cpu/src/CpuLangevinDynamics.cpp

 
-/* Portions copyright (c) 2006-2016 Stanford University and Simbios.
+/* Portions copyright (c) 2006-2017 Stanford University and Simbios.
  * Authors: Peter Eastman
  * Contributors: 
  *
@@ -29,36 +29,6 @@
 using namespace OpenMM;
 using namespace std;
 
-class CpuLangevinDynamics::Update1Task : public ThreadPool::Task {
-public:
-    Update1Task(CpuLangevinDynamics& owner) : owner(owner) {
-    }
-    void execute(ThreadPool& threads, int threadIndex) {
-        owner.threadUpdate1(threadIndex);
-    }
-    CpuLangevinDynamics& owner;
-};
-
-class CpuLangevinDynamics::Update2Task : public ThreadPool::Task {
-public:
-    Update2Task(CpuLangevinDynamics& owner) : owner(owner) {
-    }
-    void execute(ThreadPool& threads, int threadIndex) {
-        owner.threadUpdate2(threadIndex);
-    }
-    CpuLangevinDynamics& owner;
-};
-
-class CpuLangevinDynamics::Update3Task : public ThreadPool::Task {
-public:
-    Update3Task(CpuLangevinDynamics& owner) : owner(owner) {
-    }
-    void execute(ThreadPool& threads, int threadIndex) {
-        owner.threadUpdate3(threadIndex);
-    }
-    CpuLangevinDynamics& owner;
-};
-
 CpuLangevinDynamics::CpuLangevinDynamics(int numberOfAtoms, double deltaT, double friction, double temperature, ThreadPool& threads, CpuRandom& random) : 
            ReferenceStochasticDynamics(numberOfAtoms, deltaT, friction, temperature), threads(threads), random(random) {
 }
@@ -79,8 +49,7 @@ void CpuLangevinDynamics::updatePart1(int numberOfAtoms, vector<Vec3>& atomCoord
     
     // Signal the threads to start running and wait for them to finish.
     
-    Update1Task task(*this);
-    threads.execute(task);
+    threads.execute([&] (ThreadPool& threads, int threadIndex) { threadUpdate1(threadIndex); });
     threads.waitForThreads();
 }
 
@@ -97,8 +66,7 @@ void CpuLangevinDynamics::updatePart2(int numberOfAtoms, vector<Vec3>& atomCoord
     
     // Signal the threads to start running and wait for them to finish.
     
-    Update2Task task(*this);
-    threads.execute(task);
+    threads.execute([&] (ThreadPool& threads, int threadIndex) { threadUpdate2(threadIndex); });
     threads.waitForThreads();
 }
 
@@ -114,8 +82,7 @@ void CpuLangevinDynamics::updatePart3(int numberOfAtoms, vector<Vec3>& atomCoord
     
     // Signal the threads to start running and wait for them to finish.
     
-    Update3Task task(*this);
-    threads.execute(task);
+    threads.execute([&] (ThreadPool& threads, int threadIndex) { threadUpdate3(threadIndex); });
     threads.waitForThreads();
 }
 

platforms/cpu/src/CpuNeighborList.cpp

@@ -6,7 +6,7 @@
  * Biological Structures at Stanford, funded under the NIH Roadmap for        *
  * Medical Research, grant U54 GM072970. See https://simtk.org.               *
  *                                                                            *
- * Portions copyright (c) 2013-2016 Stanford University and the Authors.      *
+ * Portions copyright (c) 2013-2017 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -409,16 +409,6 @@ private:
     vector<vector<vector<pair<float, int> > > > bins;
 };
 
-class CpuNeighborList::ThreadTask : public ThreadPool::Task {
-public:
-    ThreadTask(CpuNeighborList& owner) : owner(owner) {
-    }
-    void execute(ThreadPool& threads, int threadIndex) {
-        owner.threadComputeNeighborList(threads, threadIndex);
-    }
-    CpuNeighborList& owner;
-};
-
 CpuNeighborList::CpuNeighborList(int blockSize) : blockSize(blockSize) {
 }
 
@@ -460,8 +450,7 @@ void CpuNeighborList::computeNeighborList(int numAtoms, const AlignedArray<float
     // Sort the atoms based on a Hilbert curve.
     
     atomBins.resize(numAtoms);
-    ThreadTask task(*this);
-    threads.execute(task);
+    threads.execute([&] (ThreadPool& threads, int threadIndex) { threadComputeNeighborList(threads, threadIndex); });
     threads.waitForThreads();
     sort(atomBins.begin(), atomBins.end());
 

platforms/cpu/src/CpuNonbondedForce.cpp

 
-/* Portions copyright (c) 2006-2015 Stanford University and Simbios.
+/* Portions copyright (c) 2006-2017 Stanford University and Simbios.
  * Contributors: Pande Group
  *
  * Permission is hereby granted, free of charge, to any person obtaining
@@ -30,6 +30,7 @@
 #include "ReferencePME.h"
 #include "openmm/internal/gmx_atomic.h"
 #include <algorithm>
+#include <iostream>
 
 // In case we're using some primitive version of Visual Studio this will
 // make sure that erf() and erfc() are defined.
@@ -41,23 +42,14 @@ using namespace OpenMM;
 const float CpuNonbondedForce::TWO_OVER_SQRT_PI = (float) (2/sqrt(PI_M));
 const int CpuNonbondedForce::NUM_TABLE_POINTS = 2048;
 
-class CpuNonbondedForce::ComputeDirectTask : public ThreadPool::Task {
-public:
-    ComputeDirectTask(CpuNonbondedForce& owner) : owner(owner) {
-    }
-    void execute(ThreadPool& threads, int threadIndex) {
-        owner.threadComputeDirect(threads, threadIndex);
-    }
-    CpuNonbondedForce& owner;
-};
-
 /**---------------------------------------------------------------------------------------
 
    CpuNonbondedForce constructor
 
    --------------------------------------------------------------------------------------- */
 
-CpuNonbondedForce::CpuNonbondedForce() : cutoff(false), useSwitch(false), periodic(false), ewald(false), pme(false), tableIsValid(false), cutoffDistance(0.0f), alphaEwald(0.0f) {
+CpuNonbondedForce::CpuNonbondedForce() : cutoff(false), useSwitch(false), periodic(false), ewald(false), pme(false), ljpme(false), tableIsValid(false), expTableIsValid(false),
+    cutoffDistance(0.0f), alphaDispersionEwald(0.0f), alphaEwald(0.0f) {
 }
 
 CpuNonbondedForce::~CpuNonbondedForce() {
@@ -78,11 +70,22 @@ void CpuNonbondedForce::setUseCutoff(float distance, const CpuNeighborList& neig
         tableIsValid = false;
     cutoff = true;
     cutoffDistance = distance;
+    inverseRcut6 = pow(cutoffDistance, -6);
     neighborList = &neighbors;
     krf = pow(cutoffDistance, -3.0f)*(solventDielectric-1.0)/(2.0*solventDielectric+1.0);
     crf = (1.0/cutoffDistance)*(3.0*solventDielectric)/(2.0*solventDielectric+1.0);
+    if(alphaDispersionEwald != 0.0f){
+        // We set this here, in case setUseCutoff is called after the dispersion alpha is set.
+        double dalphaR = alphaDispersionEwald*cutoffDistance;
+        double dar2 = dalphaR * dalphaR;
+        double dar4 = dar2*dar2;
+        double dar6 = dar4*dar2;
+        double expterm = EXP(-dar2);
+        inverseRcut6Expterm  = inverseRcut6*(1.0 - expterm * (1.0 + dar2 + 0.5*dar4));
     }
 
+}
+
 /**---------------------------------------------------------------------------------------
 
    Set the force to use a switching function on the Lennard-Jones interaction.
@@ -96,7 +99,7 @@ void CpuNonbondedForce::setUseSwitchingFunction(float distance) {
     switchingDistance = distance;
 }
 
-  /**---------------------------------------------------------------------------------------
+/**---------------------------------------------------------------------------------------
 
      Set the force to use periodic boundary conditions.  This requires that a cutoff has
      also been set, and the smallest side of the periodic box is at least twice the cutoff
@@ -106,7 +109,7 @@ void CpuNonbondedForce::setUseSwitchingFunction(float distance) {
 
      --------------------------------------------------------------------------------------- */
 
-  void CpuNonbondedForce::setPeriodic(Vec3* periodicBoxVectors) {
+void CpuNonbondedForce::setPeriodic(Vec3* periodicBoxVectors) {
 
     assert(cutoff);
     assert(periodicBoxVectors[0][0] >= 2.0*cutoffDistance);
@@ -126,9 +129,9 @@ void CpuNonbondedForce::setUseSwitchingFunction(float distance) {
     triclinic = (periodicBoxVectors[0][1] != 0.0 || periodicBoxVectors[0][2] != 0.0 ||
             periodicBoxVectors[1][0] != 0.0 || periodicBoxVectors[1][2] != 0.0 ||
             periodicBoxVectors[2][0] != 0.0 || periodicBoxVectors[2][1] != 0.0);
-  }
+}
 
-  /**---------------------------------------------------------------------------------------
+/**---------------------------------------------------------------------------------------
 
      Set the force to use Ewald summation.
 
@@ -139,7 +142,7 @@ void CpuNonbondedForce::setUseSwitchingFunction(float distance) {
 
      --------------------------------------------------------------------------------------- */
 
-  void CpuNonbondedForce::setUseEwald(float alpha, int kmaxx, int kmaxy, int kmaxz) {
+void CpuNonbondedForce::setUseEwald(float alpha, int kmaxx, int kmaxy, int kmaxz) {
     if (alpha != alphaEwald)
         tableIsValid = false;
     alphaEwald = alpha;
@@ -148,9 +151,9 @@ void CpuNonbondedForce::setUseSwitchingFunction(float distance) {
     numRz = kmaxz;
     ewald = true;
     tabulateEwaldScaleFactor();
-  }
+}
 
-  /**---------------------------------------------------------------------------------------
+/**---------------------------------------------------------------------------------------
 
      Set the force to use Particle-Mesh Ewald (PME) summation.
 
@@ -159,7 +162,7 @@ void CpuNonbondedForce::setUseSwitchingFunction(float distance) {
 
      --------------------------------------------------------------------------------------- */
 
-  void CpuNonbondedForce::setUsePME(float alpha, int meshSize[3]) {
+void CpuNonbondedForce::setUsePME(float alpha, int meshSize[3]) {
     if (alpha != alphaEwald)
         tableIsValid = false;
     alphaEwald = alpha;
@@ -168,10 +171,40 @@ void CpuNonbondedForce::setUseSwitchingFunction(float distance) {
     meshDim[2] = meshSize[2];
     pme = true;
     tabulateEwaldScaleFactor();
+}
+
+
+/**---------------------------------------------------------------------------------------
+
+     Set the force to use Particle-Mesh Ewald (PME) summation for dispersion.
+
+     @param alpha  the Ewald separation parameter
+     @param gridSize the dimensions of the mesh
+
+     --------------------------------------------------------------------------------------- */
+
+void CpuNonbondedForce::setUseLJPME(float alpha, int meshSize[3]) {
+    if (alpha != alphaDispersionEwald)
+        expTableIsValid = false;
+    alphaDispersionEwald = alpha;
+    dispersionMeshDim[0] = meshSize[0];
+    dispersionMeshDim[1] = meshSize[1];
+    dispersionMeshDim[2] = meshSize[2];
+    ljpme = true;
+    tabulateExpTerms();
+    if(cutoffDistance != 0.0f){
+        // We set this here, in case setUseLJPME is called after the cutoff is set
+        double dalphaR = alphaDispersionEwald*cutoffDistance;
+        double dar2 = dalphaR * dalphaR;
+        double dar4 = dar2*dar2;
+        double dar6 = dar4*dar2;
+        double expterm = EXP(-dar2);
+        inverseRcut6Expterm  = inverseRcut6*(1.0 - expterm * (1.0 + dar2 + 0.5*dar4));
     }
+}
 
 
-  void CpuNonbondedForce::tabulateEwaldScaleFactor() {
+void CpuNonbondedForce::tabulateEwaldScaleFactor() {
     if (tableIsValid)
         return;
     tableIsValid = true;
@@ -188,8 +221,28 @@ void CpuNonbondedForce::setUseSwitchingFunction(float distance) {
     }
 }
 
+void CpuNonbondedForce::tabulateExpTerms() {
+    if (expTableIsValid)
+        return;
+    expTableIsValid = true;
+    exptermsDX = cutoffDistance/NUM_TABLE_POINTS;
+    exptermsDXInv = 1.0f/exptermsDX;
+    exptermsTable.resize(NUM_TABLE_POINTS+4);
+    dExptermsTable.resize(NUM_TABLE_POINTS+4);
+    for (int i = 0; i < NUM_TABLE_POINTS+4; i++) {
+        double r = i*ewaldDX;
+        double dalphaR = alphaDispersionEwald*r;
+        double dar2 = dalphaR * dalphaR;
+        double dar4 = dar2*dar2;
+        double dar6 = dar4*dar2;
+        double expterm = EXP(-dar2);
+        exptermsTable[i]  = (1.0 - expterm * (1.0 + dar2 + 0.5*dar4));
+        dExptermsTable[i] = (1.0 - expterm * (1.0 + dar2 + 0.5*dar4 + dar6/6.0));
+    }
+}
+
 void CpuNonbondedForce::calculateReciprocalIxn(int numberOfAtoms, float* posq, const vector<Vec3>& atomCoordinates,
-                                             const vector<pair<float, float> >& atomParameters, const vector<set<int> >& exclusions,
+                                               const vector<pair<float, float> >& atomParameters, const vector<float> &C6params, const vector<set<int> >& exclusions,
                                                vector<Vec3>& forces, double* totalEnergy) const {
     typedef std::complex<float> d_complex;
 
@@ -211,6 +264,29 @@ void CpuNonbondedForce::calculateReciprocalIxn(int numberOfAtoms, float* posq, c
         if (totalEnergy)
             *totalEnergy += recipEnergy;
         pme_destroy(pmedata);
+
+        if (ljpme) {
+            // Dispersion reciprocal space terms
+            pme_init(&pmedata,alphaDispersionEwald,numberOfAtoms,dispersionMeshDim,5,1);
+
+            std::vector<Vec3> dpmeforces;
+            for (int i = 0; i < numberOfAtoms; i++){
+                charges[i] = C6params[i];
+                dpmeforces.push_back(Vec3());
+            }
+            double recipDispersionEnergy = 0.0;
+            pme_exec_dpme(pmedata,atomCoordinates,dpmeforces,charges,periodicBoxVectors,&recipDispersionEnergy);
+            for (int i = 0; i < numberOfAtoms; i++){
+                forces[i][0] -= 2.0*dpmeforces[i][0];
+                forces[i][1] -= 2.0*dpmeforces[i][1];
+                forces[i][2] -= 2.0*dpmeforces[i][2];
+            }
+            if (totalEnergy)
+                *totalEnergy += recipDispersionEnergy;
+
+            pme_destroy(pmedata);
+        }
+
     }
 
     // Ewald method
@@ -224,7 +300,7 @@ void CpuNonbondedForce::calculateReciprocalIxn(int numberOfAtoms, float* posq, c
 
         // setup K-vectors
 
-        #define EIR(x, y, z) eir[(x)*numberOfAtoms*3+(y)*3+z]
+#define EIR(x, y, z) eir[(x)*numberOfAtoms*3+(y)*3+z]
         vector<d_complex> eir(kmax*numberOfAtoms*3);
         vector<d_complex> tab_xy(numberOfAtoms);
         vector<d_complex> tab_qxyz(numberOfAtoms);
@@ -301,13 +377,14 @@ void CpuNonbondedForce::calculateReciprocalIxn(int numberOfAtoms, float* posq, c
 
 
 void CpuNonbondedForce::calculateDirectIxn(int numberOfAtoms, float* posq, const vector<Vec3>& atomCoordinates, const vector<pair<float, float> >& atomParameters,
-                const vector<set<int> >& exclusions, vector<AlignedArray<float> >& threadForce, double* totalEnergy, ThreadPool& threads) {
+                                           const vector<float>& C6params, const vector<set<int> >& exclusions, vector<AlignedArray<float> >& threadForce, double* totalEnergy, ThreadPool& threads) {
     // Record the parameters for the threads.
     
     this->numberOfAtoms = numberOfAtoms;
     this->posq = posq;
     this->atomCoordinates = &atomCoordinates[0];
     this->atomParameters = &atomParameters[0];
+    this->C6params = &C6params[0];
     this->exclusions = &exclusions[0];
     this->threadForce = &threadForce;
     includeEnergy = (totalEnergy != NULL);
@@ -318,8 +395,7 @@ void CpuNonbondedForce::calculateDirectIxn(int numberOfAtoms, float* posq, const
     
     // Signal the threads to start running and wait for them to finish.
     
-    ComputeDirectTask task(*this);
-    threads.execute(task);
+    threads.execute([&] (ThreadPool& threads, int threadIndex) { threadComputeDirect(threads, threadIndex); });
     threads.waitForThreads();
     
     // Signal the threads to subtract the exclusions.
@@ -350,9 +426,8 @@ void CpuNonbondedForce::threadComputeDirect(ThreadPool& threads, int threadIndex
     float* forces = &(*threadForce)[threadIndex][0];
     fvec4 boxSize(periodicBoxVectors[0][0], periodicBoxVectors[1][1], periodicBoxVectors[2][2], 0);
     fvec4 invBoxSize(recipBoxSize[0], recipBoxSize[1], recipBoxSize[2], 0);
-    if (ewald || pme) {
+    if (ewald || pme || ljpme) {
         // Compute the interactions from the neighbor list.
-
         while (true) {
             int nextBlock = gmx_atomic_fetch_add(reinterpret_cast<gmx_atomic_t*>(atomicCounter), 1);
             if (nextBlock >= neighborList->getNumBlocks())
@@ -395,6 +470,17 @@ void CpuNonbondedForce::threadComputeDirect(ThreadPool& threads, int threadIndex
                         }
                         else if (includeEnergy)
                             threadEnergy[threadIndex] -= alphaEwald*TWO_OVER_SQRT_PI*scaledChargeI*posq[4*j+3];
+                        if (ljpme) {
+                            float C6ij = C6params[i]*C6params[j];
+                            float inverseR2 = 1.0f/r2;
+                            float emult = C6ij*inverseR2*inverseR2*inverseR2*exptermsApprox(r);
+                            if(includeEnergy)
+                                threadEnergy[threadIndex] += emult;
+                            float dEdR = -6.0f*C6ij*inverseR2*inverseR2*inverseR2*inverseR2*dExptermsApprox(r);
+                            fvec4 result = deltaR*dEdR;
+                            (fvec4(forces+4*i)-result).store(forces+4*i);
+                            (fvec4(forces+4*j)+result).store(forces+4*j);
+                        }
                     }
                 }
             }
@@ -476,7 +562,7 @@ void CpuNonbondedForce::calculateOneIxn(int ii, int jj, float* forces, double* t
     fvec4 result = deltaR*dEdR;
     (fvec4(forces+4*ii)+result).store(forces+4*ii);
     (fvec4(forces+4*jj)-result).store(forces+4*jj);
-  }
+}
 
 void CpuNonbondedForce::getDeltaR(const fvec4& posI, const fvec4& posJ, fvec4& deltaR, float& r2, bool periodic, const fvec4& boxSize, const fvec4& invBoxSize) const {
     deltaR = posJ-posI;
@@ -502,3 +588,18 @@ float CpuNonbondedForce::erfcApprox(float x) {
     return coeff1*erfcTable[index] + coeff2*erfcTable[index+1];
 }
 
+float CpuNonbondedForce::exptermsApprox(float x) {
+    float x1 = x*exptermsDXInv;
+    int index = min((int) floor(x1), NUM_TABLE_POINTS);
+    float coeff2 = x1-index;
+    float coeff1 = 1.0f-coeff2;
+    return coeff1*exptermsTable[index] + coeff2*exptermsTable[index+1];
+}
+
+float CpuNonbondedForce::dExptermsApprox(float x) {
+    float x1 = x*exptermsDXInv;
+    int index = min((int) floor(x1), NUM_TABLE_POINTS);
+    float coeff2 = x1-index;
+    float coeff1 = 1.0f-coeff2;
+    return coeff1*dExptermsTable[index] + coeff2*dExptermsTable[index+1];
+}