Max Drude distance defaults to 0.02 nm (#3508)

* Max Drude distance defaults to 0.2 nm

* Fixed incorrect number in docs

* Fixed a test case

plugins/drude/openmmapi/include/openmm/DrudeIntegrator.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) 2008-2021 Stanford University and the Authors.      *
+ * Portions copyright (c) 2008-2022 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -72,12 +72,12 @@ public:
     void setDrudeTemperature(double temp);
     /**
      * Get the maximum distance a Drude particle can ever move from its parent particle, measured in nm.  This is implemented
-     * with a hard wall constraint.  If this distance is set to 0 (the default), the hard wall constraint is omitted.
+     * with a hard wall constraint.  The default value is 0.02.  If this distance is set to 0, the hard wall constraint is omitted.
      */
     double getMaxDrudeDistance() const;
     /**
      * Set the maximum distance a Drude particle can ever move from its parent particle, measured in nm.  This is implemented
-     * with a hard wall constraint.  If this distance is set to 0 (the default), the hard wall constraint is omitted.
+     * with a hard wall constraint.  The default value is 0.02.  If this distance is set to 0, the hard wall constraint is omitted.
      */
     void setMaxDrudeDistance(double distance);
     /**

plugins/drude/openmmapi/include/openmm/DrudeLangevinIntegrator.h

@@ -47,7 +47,7 @@ namespace OpenMM {
  *
  * This integrator can optionally set an upper limit on how far any Drude particle is ever allowed to
  * get from its parent particle.  This can sometimes help to improve stability.  The limit is enforced
- * with a hard wall constraint.
+ * with a hard wall constraint.  By default the limit is set to 0.02 nm.
  * 
  * This Integrator requires the System to include a DrudeForce, which it uses to identify the Drude
  * particles.

plugins/drude/openmmapi/include/openmm/DrudeNoseHooverIntegrator.h

@@ -45,6 +45,10 @@ namespace OpenMM {
  * A second thermostat, typically with a much lower temperature, is applied to the relative internal
  * displacement of each pair.
  *
+ * This integrator can optionally set an upper limit on how far any Drude particle is ever allowed to
+ * get from its parent particle.  This can sometimes help to improve stability.  The limit is enforced
+ * with a hard wall constraint.  By default the limit is set to 0.02 nm.
+ *
  * This Integrator requires the System to include a DrudeForce, which it uses to identify the Drude
  * particles.
  */

plugins/drude/openmmapi/src/DrudeLangevinIntegrator.cpp

@@ -52,7 +52,7 @@ DrudeLangevinIntegrator::DrudeLangevinIntegrator(double temperature, double fric
     setFriction(frictionCoeff);
     setDrudeTemperature(drudeTemperature);
     setDrudeFriction(drudeFrictionCoeff);
-    setMaxDrudeDistance(0);
+    setMaxDrudeDistance(0.02);
     setStepSize(stepSize);
     setConstraintTolerance(1e-5);
     setRandomNumberSeed(0);

plugins/drude/openmmapi/src/DrudeNoseHooverIntegrator.cpp

@@ -54,10 +54,8 @@ namespace OpenMM {
 DrudeNoseHooverIntegrator::DrudeNoseHooverIntegrator(double temperature, double collisionFrequency, 
                                                      double drudeTemperature, double drudeCollisionFrequency,
                                                      double stepSize, int chainLength, int numMTS, int numYoshidaSuzuki) :
-    NoseHooverIntegrator(stepSize),
-    drudeTemperature(drudeTemperature)
-{
-    setMaxDrudeDistance(0);
+            NoseHooverIntegrator(stepSize), drudeTemperature(drudeTemperature) {
+    setMaxDrudeDistance(0.02);
     hasSubsystemThermostats_ = false;
     addSubsystemThermostat(std::vector<int>(), std::vector<std::pair<int, int>>(), temperature,
                            collisionFrequency, drudeTemperature, drudeCollisionFrequency,

plugins/drude/openmmapi/src/DrudeSCFIntegrator.cpp

@@ -48,6 +48,7 @@ DrudeSCFIntegrator::DrudeSCFIntegrator(double stepSize) : DrudeIntegrator(stepSi
     setStepSize(stepSize);
     setMinimizationErrorTolerance(0.1);
     setConstraintTolerance(1e-5);
+    setMaxDrudeDistance(0.0);
 }
 
 void DrudeSCFIntegrator::initialize(ContextImpl& contextRef) {
@@ -64,6 +65,8 @@ void DrudeSCFIntegrator::initialize(ContextImpl& contextRef) {
         }
     if (force == NULL)
         throw OpenMMException("The System does not contain a DrudeForce");
+    if (getMaxDrudeDistance() != 0.0)
+        throw OpenMMException("DrudeSCFIntegrator does not currently support setting max Drude distance");
     context = &contextRef;
     owner = &contextRef.getOwner();
     kernel = context->getPlatform().createKernel(IntegrateDrudeSCFStepKernel::Name(), contextRef);

wrappers/python/tests/TestAPIUnits.py

@@ -1051,7 +1051,7 @@ class TestAPIUnits(unittest.TestCase):
         self.assertEqual(integrator.getStepSize(), 0.1*femtosecond)
         integrator.setStepSize(0.0005)
         self.assertEqual(integrator.getStepSize(), 0.0005*picosecond)
-        self.assertEqual(integrator.getMaxDrudeDistance(), 0*nanometer)
+        self.assertEqual(integrator.getMaxDrudeDistance(), 0.02*nanometer)
         integrator.setMaxDrudeDistance(0.05)
         self.assertEqual(integrator.getMaxDrudeDistance(), 0.05*nanometer)