Thanks to Chris, we now know that the Langevin friction parameter is in ONE...

Thanks to Chris, we now know that the Langevin friction parameter is in ONE OVER picoseconds, NOT picoseconds!!

examples/HelloSodiumChloride.cpp

@@ -24,7 +24,7 @@ using std::printf;
 //                   MODELING AND SIMULATION PARAMETERS
 // -----------------------------------------------------------------------------
 static const double Temperature         = 300;     // Kelvins
-static const double FrictionInPs        = 1./91.;  // picoseconds between collisions
+static const double FrictionInPerPs     = 91.;     // collisions per picosecond
 static const double SolventDielectric   = 80.;     // typical for water
 static const double SoluteDielectric    = 2.;      // typical for protein
 
@@ -119,7 +119,7 @@ int main() {
         std::string   platformName;
 
         // Set up OpenMM data structures; returns OpenMM Platform name.
-        MyOpenMMData* omm = myInitializeOpenMM(atoms, Temperature, FrictionInPs,
+        MyOpenMMData* omm = myInitializeOpenMM(atoms, Temperature, FrictionInPerPs,
                                                SolventDielectric, SoluteDielectric,
                                                StepSizeInFs, platformName);
 

examples/HelloSodiumChlorideInC.c

@@ -25,7 +25,7 @@
  *                   MODELING AND SIMULATION PARAMETERS
  * -------------------------------------------------------------------------- */
 static const double Temperature         = 300;    /*Kelvins */
-static const double FrictionInPs        = 1./91.; /*ps between collisions*/
+static const double FrictionInPerPs     = 91.;    /*collisions per ps*/
 static const double SolventDielectric   = 80.;    /*typical for water    */
 static const double SoluteDielectric    = 2.;     /*typical for protein  */
 
@@ -124,7 +124,7 @@ int main() {
     const char*   platformName;
 
     // Set up OpenMM data structures; returns OpenMM Platform name.
-    MyOpenMMData* omm = myInitializeOpenMM(atoms, Temperature, FrictionInPs,
+    MyOpenMMData* omm = myInitializeOpenMM(atoms, Temperature, FrictionInPerPs,
                                            SolventDielectric, SoluteDielectric,
                                            StepSizeInFs, &platformName);
 
@@ -187,7 +187,7 @@ struct MyOpenMMData_s {
 static MyOpenMMData* 
 myInitializeOpenMM( const MyAtomInfo    atoms[],
                     double              temperature,
-                    double              frictionInPs,
+                    double              frictionInPerPs,
                     double              solventDielectric,
                     double              soluteDielectric,
                     double              stepSizeInFs, 
@@ -252,7 +252,7 @@ myInitializeOpenMM( const MyAtomInfo    atoms[],
      * positions we collected above. Initial velocities will be zero but could
      * have been set here. */
     omm->integrator = (OpenMM_Integrator*)OpenMM_LangevinIntegrator_create(
-                                            temperature, frictionInPs, 
+                                            temperature, frictionInPerPs, 
                                             stepSizeInFs * OpenMM_PsPerFs);
     omm->context    = OpenMM_Context_create(omm->system, omm->integrator);
     OpenMM_Context_setPositions(omm->context, initialPosInNm);

examples/HelloWorld.cpp

@@ -33,7 +33,7 @@ static AtomInfo atoms[] = {
 };
 
 static const double Temperature         = 100;   // Kelvins
-static const double Friction            = 1./91.;  // picoseconds between collisions
+static const double FrictionInPerPs     = 91.;   // collisions per ps
 static const double StepSizeFs          = 2;     // femtoseconds
 static const double ReportIntervalFs    = 1000;
 static const double SimulationTimePs    = 1000;  // total simulation time (ps)

examples/wrappers/OpenMM_CWrapper.cpp

@@ -333,10 +333,10 @@ void openmm_verletintegrator_step_(OpenMM_VerletIntegrator* const& verlet, int&
 
 
     // OpenMM::LangevinIntegrator
-OpenMM_LangevinIntegrator* OpenMM_LangevinIntegrator_create(double temperature, double frictionInPs, double stepSzInPs) 
-{   return (OpenMM_LangevinIntegrator*)new LangevinIntegrator(temperature, frictionInPs, stepSzInPs); }
-void openmm_langevinintegrator_create_(OpenMM_LangevinIntegrator*& langevin, double& temperature, double& frictionInPs, double& stepSzInPs)
-{   langevin = OpenMM_LangevinIntegrator_create(temperature, frictionInPs, stepSzInPs); }
+OpenMM_LangevinIntegrator* OpenMM_LangevinIntegrator_create(double temperature, double frictionInPerPs, double stepSzInPs) 
+{   return (OpenMM_LangevinIntegrator*)new LangevinIntegrator(temperature, frictionInPerPs, stepSzInPs); }
+void openmm_langevinintegrator_create_(OpenMM_LangevinIntegrator*& langevin, double& temperature, double& frictionInPerPs, double& stepSzInPs)
+{   langevin = OpenMM_LangevinIntegrator_create(temperature, frictionInPerPs, stepSzInPs); }
 
 void OpenMM_LangevinIntegrator_destroy(OpenMM_LangevinIntegrator* doomed) 
 {   delete (LangevinIntegrator*)doomed; }

examples/wrappers/OpenMM_CWrapper.h

-// -----------------------------------------------------------------------------
-//        OpenMM(tm) example C wrapper function declarations (June 2009)
-// -----------------------------------------------------------------------------
-// This header should be included by a C main program that would like to
-// access the OpenMM API through the C wrappers. Please note that this is not
-// an official part of OpenMM; it is just an example of how the C++ API can be
-// wrapped for access from C.
-// -----------------------------------------------------------------------------
-
-#ifndef OPENMM_CWRAPPER_H
-#define OPENMM_CWRAPPER_H
-
-#if defined(__cplusplus)
-    #include <cmath>
-#else
-    #include <math.h>
-#endif
-
-/*
- * This header file is intended to be included in a C compilation unit so must
- * not use any C++ features that are not also present in ANSI C.
- */
+/* --------------------------------------------------------------------------
+ *       OpenMM(tm) example C wrapper function declarations (June 2009)
+ * --------------------------------------------------------------------------
+ * This header should be included by a C main program that would like to
+ * access the OpenMM API through the C wrappers. Please note that this is not
+ * an official part of OpenMM; it is just an example of how the C++ API can
+ * be wrapped for access from C.
+ *
+ * Note: this header must be includable in both ANSI C and C++ code, because
+ * the function declarations must be common to both the users and the
+ * implementing code, which is in C++.
+ * -------------------------------------------------------------------------- */
+
+#ifndef OPENMM_CWRAPPER_H_
+#define OPENMM_CWRAPPER_H_
+
+//#if defined(__cplusplus)
+//    #include <cmath>
+//#else
+//    #include <math.h>
+//#endif
 
 /* These incomplete types are declared so we can have unique pointer types. */
 typedef struct OpenMM_System_s      OpenMM_System;
@@ -168,7 +167,7 @@ extern OpenMM_VerletIntegrator* OpenMM_VerletIntegrator_create(double stepSzInPs
 extern void                     OpenMM_VerletIntegrator_destroy(OpenMM_VerletIntegrator*);
 extern void                     OpenMM_VerletIntegrator_step(OpenMM_VerletIntegrator*, int numSteps);
 /* OpenMM::LangevinIntegrator */
-extern OpenMM_LangevinIntegrator* OpenMM_LangevinIntegrator_create(double temperature, double frictionInPs, double stepSzInPs);
+extern OpenMM_LangevinIntegrator* OpenMM_LangevinIntegrator_create(double temperature, double frictionInPerPs, double stepSzInPs);
 extern void                       OpenMM_VLangevinIntegrator_destroy(OpenMM_LangevinIntegrator*);
 extern void                       OpenMM_LangevinIntegrator_step(OpenMM_LangevinIntegrator*, int numSteps);
 
@@ -204,7 +203,7 @@ static void OpenMM_Vec3_set(double x, double y, double z, OpenMM_Vec3 out) {
 }
 
 
-#endif /*OPENMM_CWRAPPER_H*/
+#endif /*OPENMM_CWRAPPER_H_*/