Drude integrators can find DrudeForce inside another force (#5054)

openmmapi/include/openmm/internal/ATMForceImpl.h

@@ -36,7 +36,7 @@ public:
     std::vector<std::pair<int, int> > getBondedParticles() const;
     void updateParametersInContext(ContextImpl& context);
     void getPerturbationEnergy(ContextImpl& context, double& u1, double& u0, double& energy);
-
+    std::vector<const Force*> getContainedForces() const;
 private:
     const ATMForce& owner;
     Kernel kernel;

openmmapi/include/openmm/internal/CustomCVForceImpl.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) 2008-2022 Stanford University and the Authors.      *
+ * Portions copyright (c) 2008-2025 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -66,6 +66,7 @@ public:
     void getCollectiveVariableValues(ContextImpl& context, std::vector<double>& values);
     Context& getInnerContext();
     void updateParametersInContext(ContextImpl& context);
+    std::vector<const Force*> getContainedForces() const;
 private:
     const CustomCVForce& owner;
     Kernel kernel;

openmmapi/include/openmm/internal/ForceImpl.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) 2008 Stanford University and the Authors.           *
+ * Portions copyright (c) 2008-2025 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -112,6 +112,11 @@ public:
     virtual std::vector<std::pair<int, int> > getBondedParticles() const {
         return std::vector<std::pair<int, int> >(0);
     }
+    /**
+     * Some Forces may themselves contain other Forces.  This returns any Forces contained by
+     * this one.  The default implementation returns an empty vector.
+     */
+    virtual std::vector<const Force*> getContainedForces() const;
 protected:
     /**
      * Get the ContextImpl corresponding to a Context.

openmmapi/src/ATMForceImpl.cpp

@@ -9,7 +9,7 @@
  * https://github.com/Gallicchio-Lab/openmm-atmmetaforce-plugin               *
  * with support from the National Science Foundation CAREER 1750511           *
  *                                                                            *
- * Portions copyright (c) 2021-2024 by the Authors                            *
+ * Portions copyright (c) 2021-2025 by the Authors                            *
  * Authors: Emilio Gallicchio                                                 *
  * Contributors: Peter Eastman                                                *
  *                                                                            *
@@ -203,3 +203,10 @@ void ATMForceImpl::getPerturbationEnergy(ContextImpl& context, double& u1, doubl
     u1 = state1Energy;
     energy = combinedEnergy;
 }
+
+vector<const Force*> ATMForceImpl::getContainedForces() const {
+    vector<const Force*> forces;
+    for (int i = 0; i < owner.getNumForces(); i++)
+        forces.push_back(&owner.getForce(i));
+    return forces;
+}

openmmapi/src/CustomCVForceImpl.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) 2008-2022 Stanford University and the Authors.      *
+ * Portions copyright (c) 2008-2025 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -127,3 +127,10 @@ void CustomCVForceImpl::updateParametersInContext(ContextImpl& context) {
     kernel.getAs<CalcCustomCVForceKernel>().copyParametersToContext(context, owner);
     context.systemChanged();
 }
+
+vector<const Force*> CustomCVForceImpl::getContainedForces() const {
+    vector<const Force*> forces;
+    for (int i = 0; i < owner.getNumCollectiveVariables(); i++)
+        forces.push_back(&owner.getCollectiveVariable(i));
+    return forces;
+}

openmmapi/src/ForceImpl.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) 2017 Stanford University and the Authors.           *
+ * Portions copyright (c) 2017-2025 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -44,3 +44,7 @@ void ForceImpl::updateContextState(ContextImpl& context, bool& forcesInvalid) {
 
 void ForceImpl::updateContextState(ContextImpl& context) {
 }
+
+vector<const Force*> ForceImpl::getContainedForces() const {
+    return {};
+}

plugins/drude/openmmapi/include/openmm/internal/DrudeHelpers.h

+#ifndef OPENMM_DRUDEHELPERS_H_
+#define OPENMM_DRUDEHELPERS_H_
+
+/* -------------------------------------------------------------------------- *
+ *                                   OpenMM                                   *
+ * -------------------------------------------------------------------------- *
+ * This is part of the OpenMM molecular simulation toolkit originating from   *
+ * Simbios, the NIH National Center for Physics-Based Simulation of           *
+ * Biological Structures at Stanford, funded under the NIH Roadmap for        *
+ * Medical Research, grant U54 GM072970. See https://simtk.org.               *
+ *                                                                            *
+ * Portions copyright (c) 2008-2025 Stanford University and the Authors.      *
+ * Authors: Peter Eastman                                                     *
+ * Contributors:                                                              *
+ *                                                                            *
+ * Permission is hereby granted, free of charge, to any person obtaining a    *
+ * copy of this software and associated documentation files (the "Software"), *
+ * to deal in the Software without restriction, including without limitation  *
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,   *
+ * and/or sell copies of the Software, and to permit persons to whom the      *
+ * Software is furnished to do so, subject to the following conditions:       *
+ *                                                                            *
+ * The above copyright notice and this permission notice shall be included in *
+ * all copies or substantial portions of the Software.                        *
+ *                                                                            *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR *
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,   *
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL    *
+ * THE AUTHORS, CONTRIBUTORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,    *
+ * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR      *
+ * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE  *
+ * USE OR OTHER DEALINGS IN THE SOFTWARE.                                     *
+ * -------------------------------------------------------------------------- */
+
+#include "openmm/DrudeForce.h"
+#include "openmm/System.h"
+#include "openmm/internal/ContextImpl.h"
+
+namespace OpenMM {
+
+/**
+ * Find the DrudeForce contained in the System.
+ */
+const DrudeForce* getDrudeForce(const ContextImpl& context);
+
+/**
+ * Identify normal particles (not part of a pair) and Drude particle pairs.
+ */
+void findParticlesAndPairs(const ContextImpl& context, std::vector<int>& normalParticles, std::vector<std::pair<int, int> >& pairParticles);
+
+std::vector<Vec3> assignDrudeVelocities(const ContextImpl& context, double temperature, double drudeTemperature, int randomSeed);
+
+/**
+ * Computes the instantaneous temperatures of the system and the internal Drude motion and returns a pair (T_system, T_drude)
+ */
+std::pair<double, double> computeTemperaturesFromVelocities(const ContextImpl& context, const std::vector<Vec3>& velocities);
+
+}
+
+#endif /*OPENMM_DRUDEHELPERS_H_*/

plugins/drude/openmmapi/src/DrudeHelpers.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) 2008-2023 Stanford University and the Authors.      *
+ * Portions copyright (c) 2008-2025 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -29,14 +29,14 @@
  * USE OR OTHER DEALINGS IN THE SOFTWARE.                                     *
  * -------------------------------------------------------------------------- */
 
+#include "openmm/internal/DrudeHelpers.h"
 #include "sfmt/SFMT.h"
 #include "SimTKOpenMMRealType.h"
 #include "openmm/CMMotionRemover.h"
-#include "openmm/DrudeForce.h"
 #include "openmm/DrudeLangevinIntegrator.h"
 #include "openmm/Context.h"
-#include "openmm/System.h"
 #include "openmm/OpenMMException.h"
+#include "openmm/internal/ForceImpl.h"
 
 #include <set>
 
@@ -45,20 +45,42 @@ using namespace std;
 namespace OpenMM {
 
 /**
- * Identify normal particles (not part of a pair) and Drude particle pairs.
+ * Find the DrudeForce contained in the System.
  */
-void findParticlesAndPairs(const System &system, vector<int>& normalParticles, vector<pair<int, int> >& pairParticles) {
-    // Find the underlying Drude force object
-    const DrudeForce* drudeForce = NULL;
+const DrudeForce* getDrudeForce(const ContextImpl& context) {
+    const DrudeForce* force = NULL;
+    const System& system = context.getSystem();
     for (int i = 0; i < system.getNumForces(); i++)
         if (dynamic_cast<const DrudeForce*>(&system.getForce(i)) != NULL) {
-            if (drudeForce == NULL)
-                drudeForce = dynamic_cast<const DrudeForce*>(&system.getForce(i));
+            if (force == NULL)
+                force = dynamic_cast<const DrudeForce*>(&system.getForce(i));
             else
                 throw OpenMMException("The System contains multiple DrudeForces");
         }
-    if (drudeForce == NULL)
-        throw OpenMMException("The System does not contain a DrudeForce");
+    if (force != NULL)
+        return force;
+
+    // The System doesn't directly contain a DrudeForce.  Look for one inside another force.
+
+    for (const ForceImpl* impl : context.getForceImpls())
+        for (const Force* f : impl->getContainedForces())
+            if (dynamic_cast<const DrudeForce*>(f) != NULL) {
+                if (force == NULL)
+                    force = dynamic_cast<const DrudeForce*>(f);
+                else
+                    throw OpenMMException("The System contains multiple DrudeForces");
+            }
+    if (force != NULL)
+        return force;
+    throw OpenMMException("The System does not contain a DrudeForce");
+}
+
+/**
+ * Identify normal particles (not part of a pair) and Drude particle pairs.
+ */
+void findParticlesAndPairs(const ContextImpl& context, vector<int>& normalParticles, vector<pair<int, int> >& pairParticles) {
+    const System& system = context.getSystem();
+    const DrudeForce* drudeForce = getDrudeForce(context);
 
     // Figure out which particles are individual and which are Drude pairs
     set<int> particles;
@@ -75,10 +97,11 @@ void findParticlesAndPairs(const System &system, vector<int>& normalParticles, v
     normalParticles.insert(normalParticles.begin(), particles.begin(), particles.end());
 }
 
-vector<Vec3> assignDrudeVelocities(const System &system, double temperature, double drudeTemperature, int randomSeed) {
+vector<Vec3> assignDrudeVelocities(const ContextImpl& context, double temperature, double drudeTemperature, int randomSeed) {
+    const System& system = context.getSystem();
     vector<int> normalParticles;
     vector<pair<int, int> > pairParticles;
-    findParticlesAndPairs(system, normalParticles, pairParticles);
+    findParticlesAndPairs(context, normalParticles, pairParticles);
 
     // Generate the list of Gaussian random numbers.
     OpenMM_SFMT::SFMT sfmt;
@@ -135,10 +158,11 @@ vector<Vec3> assignDrudeVelocities(const System &system, double temperature, dou
 /**
  * Computes the instantaneous temperatures of the system and the internal Drude motion and returns a pair (T_system, T_drude)
  */
-pair<double, double> computeTemperaturesFromVelocities(const System& system, const vector<Vec3>& velocities) {
+pair<double, double> computeTemperaturesFromVelocities(const ContextImpl& context, const vector<Vec3>& velocities) {
+    const System& system = context.getSystem();
     vector<int> normalParticles;
     vector<pair<int, int> > pairParticles;
-    findParticlesAndPairs(system, normalParticles, pairParticles);
+    findParticlesAndPairs(context, normalParticles, pairParticles);
     double energy = 0.0, drudeEnergy = 0;
     int dof = 0, drudeDof = 0;
     

plugins/drude/openmmapi/src/DrudeIntegrator.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) 2008-2021 Stanford University and the Authors.      *
+ * Portions copyright (c) 2008-2025 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -34,17 +34,13 @@
 #include "openmm/DrudeIntegrator.h"
 #include "openmm/OpenMMException.h"
 #include "openmm/System.h"
-
+#include "openmm/internal/DrudeHelpers.h"
 #include <set>
 
 using namespace OpenMM;
 
-namespace OpenMM {
-    extern std::vector<Vec3> assignDrudeVelocities(const System &system, double temperature, double drudeTemperature, int randomSeed);
-}
-
 std::vector<Vec3> DrudeIntegrator::getVelocitiesForTemperature(const System &system, double temperature, int randomSeedIn) const {
-    return assignDrudeVelocities(system, temperature, drudeTemperature, randomSeedIn);
+    return assignDrudeVelocities(*context, temperature, drudeTemperature, randomSeedIn);
 }
 
 void DrudeIntegrator::setDrudeTemperature(double temp) {

plugins/drude/openmmapi/src/DrudeLangevinIntegrator.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) 2008-2022 Stanford University and the Authors.      *
+ * Portions copyright (c) 2008-2025 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -32,8 +32,9 @@
 #include "openmm/DrudeLangevinIntegrator.h"
 #include "openmm/Context.h"
 #include "openmm/OpenMMException.h"
-#include "openmm/internal/ContextImpl.h"
 #include "openmm/DrudeKernels.h"
+#include "openmm/internal/ContextImpl.h"
+#include "openmm/internal/DrudeHelpers.h"
 #include <cmath>
 #include <ctime>
 #include <set>
@@ -44,10 +45,6 @@ using std::string;
 using std::vector;
 using std::pair;
 
-namespace OpenMM {
-	pair<double, double> computeTemperaturesFromVelocities(const System& system, const vector<Vec3>& velocities);
-}
-
 DrudeLangevinIntegrator::DrudeLangevinIntegrator(double temperature, double frictionCoeff, double drudeTemperature, double drudeFrictionCoeff, double stepSize) : DrudeIntegrator(stepSize) {
     setTemperature(temperature);
     setFriction(frictionCoeff);
@@ -62,17 +59,7 @@ DrudeLangevinIntegrator::DrudeLangevinIntegrator(double temperature, double fric
 void DrudeLangevinIntegrator::initialize(ContextImpl& contextRef) {
     if (owner != NULL && &contextRef.getOwner() != owner)
         throw OpenMMException("This Integrator is already bound to a context");
-    const DrudeForce* force = NULL;
-    const System& system = contextRef.getSystem();
-    for (int i = 0; i < system.getNumForces(); i++)
-        if (dynamic_cast<const DrudeForce*>(&system.getForce(i)) != NULL) {
-            if (force == NULL)
-                force = dynamic_cast<const DrudeForce*>(&system.getForce(i));
-            else
-                throw OpenMMException("The System contains multiple DrudeForces");
-        }
-    if (force == NULL)
-        throw OpenMMException("The System does not contain a DrudeForce");
+    const DrudeForce* force = getDrudeForce(contextRef);
     context = &contextRef;
     owner = &contextRef.getOwner();
     kernel = context->getPlatform().createKernel(IntegrateDrudeLangevinStepKernel::Name(), contextRef);
@@ -127,7 +114,7 @@ double DrudeLangevinIntegrator::computeSystemTemperature() {
     context->calcForcesAndEnergy(true, false, getIntegrationForceGroups());
     vector<Vec3> velocities;
     context->computeShiftedVelocities(getVelocityTimeOffset(), velocities);
-    return computeTemperaturesFromVelocities(context->getSystem(), velocities).first;
+    return computeTemperaturesFromVelocities(*context, velocities).first;
 }
 
 double DrudeLangevinIntegrator::computeDrudeTemperature() {
@@ -136,6 +123,6 @@ double DrudeLangevinIntegrator::computeDrudeTemperature() {
     context->calcForcesAndEnergy(true, false, getIntegrationForceGroups());
     vector<Vec3> velocities;
     context->computeShiftedVelocities(getVelocityTimeOffset(), velocities);
-    return computeTemperaturesFromVelocities(context->getSystem(), velocities).second;
+    return computeTemperaturesFromVelocities(*context, velocities).second;
 } 
 

plugins/drude/openmmapi/src/DrudeNoseHooverIntegrator.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) 2019-2022 Stanford University and the Authors.      *
+ * Portions copyright (c) 2019-2025 Stanford University and the Authors.      *
  * Authors: Andreas Krämer and Andrew C. Simmonett                            *
  * Contributors: Peter Eastman                                                *
  *                                                                            *
@@ -33,11 +33,12 @@
 #include "SimTKOpenMMRealType.h"
 #include "openmm/Context.h"
 #include "openmm/OpenMMException.h"
-#include "openmm/internal/ContextImpl.h"
 #include "openmm/DrudeKernels.h"
 #include "openmm/DrudeForce.h"
 #include "openmm/CMMotionRemover.h"
 #include "openmm/kernels.h"
+#include "openmm/internal/ContextImpl.h"
+#include "openmm/internal/DrudeHelpers.h"
 #include <ctime>
 #include <iostream>
 #include <string>
@@ -48,12 +49,6 @@ using std::string;
 using std::vector;
 using std::pair;
 
-namespace OpenMM {
-    extern std::vector<Vec3> assignDrudeVelocities(const System &system, double temperature, double drudeTemperature, int randomSeed);
-    pair<double, double> computeTemperaturesFromVelocities(const System& system, const vector<Vec3>& velocities);
-}
-
-
 DrudeNoseHooverIntegrator::DrudeNoseHooverIntegrator(double temperature, double collisionFrequency, 
                                                      double drudeTemperature, double drudeCollisionFrequency,
                                                      double stepSize, int chainLength, int numMTS, int numYoshidaSuzuki) :
@@ -90,22 +85,14 @@ void DrudeNoseHooverIntegrator::initialize(ContextImpl& contextRef) {
 
     // check for drude particles and build the Nose-Hoover Chains
     const System& system = context->getSystem();
-    const DrudeForce* drudeForce = NULL;
+    const DrudeForce* drudeForce = getDrudeForce(contextRef);
 
-    bool hasCMMotionRemover = false;
-    for (int i = 0; i < system.getNumForces(); i++){
-        if (dynamic_cast<const DrudeForce*>(&system.getForce(i)) != NULL) {
-            if (drudeForce == NULL)
-                drudeForce = dynamic_cast<const DrudeForce*>(&system.getForce(i));
-            else
-                throw OpenMMException("The System contains multiple DrudeForces");
-        }
-        if (dynamic_cast<const CMMotionRemover*>(&system.getForce(i))) {
-            hasCMMotionRemover = true;
-        }
-    }
     if (drudeForce == NULL)
         throw OpenMMException("The System does not contain a DrudeForce");
+    bool hasCMMotionRemover = false;
+    for (int i = 0; i < system.getNumForces(); i++)
+        if (dynamic_cast<const CMMotionRemover*>(&system.getForce(i)))
+            hasCMMotionRemover = true;
     if (!hasCMMotionRemover) {
         std::cout << "Warning: Did not find a center-of-mass motion remover in the system. "
                      "This is problematic when using Drude." << std::endl;
@@ -154,7 +141,7 @@ double DrudeNoseHooverIntegrator::computeSystemTemperature() {
     context->calcForcesAndEnergy(true, false, getIntegrationForceGroups());
     vector<Vec3> velocities;
     context->computeShiftedVelocities(getVelocityTimeOffset(), velocities);
-    return computeTemperaturesFromVelocities(context->getSystem(), velocities).first;
+    return computeTemperaturesFromVelocities(*context, velocities).first;
 }
 
 double DrudeNoseHooverIntegrator::computeDrudeTemperature() {
@@ -170,6 +157,6 @@ double DrudeNoseHooverIntegrator::computeDrudeTemperature() {
 
 std::vector<Vec3> DrudeNoseHooverIntegrator::getVelocitiesForTemperature(const System &system, double temperature,
                                                                          int randomSeedIn) const {
-    return assignDrudeVelocities(system, temperature, drudeTemperature, randomSeedIn);
+    return assignDrudeVelocities(*context, temperature, drudeTemperature, randomSeedIn);
 }
 

plugins/drude/openmmapi/src/DrudeSCFIntegrator.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) 2008-2023 Stanford University and the Authors.      *
+ * Portions copyright (c) 2008-2025 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -30,10 +30,11 @@
  * -------------------------------------------------------------------------- */
 
 #include "openmm/DrudeSCFIntegrator.h"
+#include "openmm/DrudeKernels.h"
 #include "openmm/Context.h"
 #include "openmm/OpenMMException.h"
 #include "openmm/internal/ContextImpl.h"
-#include "openmm/DrudeKernels.h"
+#include "openmm/internal/DrudeHelpers.h"
 #include <cmath>
 #include <ctime>
 #include <string>
@@ -54,17 +55,7 @@ DrudeSCFIntegrator::DrudeSCFIntegrator(double stepSize) : DrudeIntegrator(stepSi
 void DrudeSCFIntegrator::initialize(ContextImpl& contextRef) {
     if (owner != NULL && &contextRef.getOwner() != owner)
         throw OpenMMException("This Integrator is already bound to a context");
-    const DrudeForce* force = NULL;
-    const System& system = contextRef.getSystem();
-    for (int i = 0; i < system.getNumForces(); i++)
-        if (dynamic_cast<const DrudeForce*>(&system.getForce(i)) != NULL) {
-            if (force == NULL)
-                force = dynamic_cast<const DrudeForce*>(&system.getForce(i));
-            else
-                throw OpenMMException("The System contains multiple DrudeForces");
-        }
-    if (force == NULL)
-        throw OpenMMException("The System does not contain a DrudeForce");
+    const DrudeForce* force = getDrudeForce(contextRef);
     if (getMaxDrudeDistance() != 0.0)
         throw OpenMMException("DrudeSCFIntegrator does not currently support setting max Drude distance");
     context = &contextRef;

plugins/drude/tests/TestDrudeLangevinIntegrator.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) 2013-2016 Stanford University and the Authors.      *
+ * Portions copyright (c) 2013-2025 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -31,6 +31,7 @@
 
 #include "openmm/internal/AssertionUtilities.h"
 #include "openmm/Context.h"
+#include "openmm/CustomCVForce.h"
 #include "openmm/NonbondedForce.h"
 #include "openmm/Platform.h"
 #include "openmm/System.h"
@@ -44,7 +45,7 @@
 using namespace OpenMM;
 using namespace std;
 
-void testSinglePair() {
+void testSinglePair(bool contained) {
     const double temperature = 300.0;
     const double temperatureDrude = 10.0;
     const double k = ONE_4PI_EPS0*1.5;
@@ -60,7 +61,13 @@ void testSinglePair() {
     system.addParticle(mass2);
     DrudeForce* drude = new DrudeForce();
     drude->addParticle(1, 0, -1, -1, -1, charge, alpha, 1, 1);
-    system.addForce(drude);
+    if (contained) {
+        CustomCVForce* cv = new CustomCVForce("x");
+        cv->addCollectiveVariable("x", drude);
+        system.addForce(cv);
+    }
+    else
+        system.addForce(drude);
     vector<Vec3> positions(2);
     positions[0] = Vec3(0, 0, 0);
     positions[1] = Vec3(0, 0, 0);
@@ -297,10 +304,11 @@ void runPlatformTests();
 int main(int argc, char* argv[]) {
     try {
         setupKernels(argc, argv);
-        testInitialTemperature();
-        testSinglePair();
+        testSinglePair(false);
+        testSinglePair(true);
         testWater();
         testForceEnergyConsistency();
+        testInitialTemperature();
         runPlatformTests();
     }
     catch(const std::exception& e) {