PeriodicTorsionForce
¶

class PeriodicTorsionForce : public OpenMM::Force¶
This class implements an interaction between groups of four particles that varies periodically with the torsion angle between them. To use it, create a PeriodicTorsionForce object then call addTorsion() once for each torsion. After a torsion has been added, you can modify its force field parameters by calling setTorsionParameters(). This will have no effect on Contexts that already exist unless you call updateParametersInContext().
Public Functions

PeriodicTorsionForce()¶
Create a PeriodicTorsionForce.

inline int getNumTorsions() const¶
Get the number of periodic torsion terms in the potential function

int addTorsion(int particle1, int particle2, int particle3, int particle4, int periodicity, double phase, double k)¶
Add a periodic torsion term to the force field.
 Parameters
particle1 – the index of the first particle forming the torsion
particle2 – the index of the second particle forming the torsion
particle3 – the index of the third particle forming the torsion
particle4 – the index of the fourth particle forming the torsion
periodicity – the periodicity of the torsion
phase – the phase offset of the torsion, measured in radians
k – the force constant for the torsion
 Returns
the index of the torsion that was added

void getTorsionParameters(int index, int &particle1, int &particle2, int &particle3, int &particle4, int &periodicity, double &phase, double &k) const¶
Get the force field parameters for a periodic torsion term.
 Parameters
index – the index of the torsion for which to get parameters
particle1 – [out] the index of the first particle forming the torsion
particle2 – [out] the index of the second particle forming the torsion
particle3 – [out] the index of the third particle forming the torsion
particle4 – [out] the index of the fourth particle forming the torsion
periodicity – [out] the periodicity of the torsion
phase – [out] the phase offset of the torsion, measured in radians
k – [out] the force constant for the torsion

void setTorsionParameters(int index, int particle1, int particle2, int particle3, int particle4, int periodicity, double phase, double k)¶
Set the force field parameters for a periodic torsion term.
 Parameters
index – the index of the torsion for which to set parameters
particle1 – the index of the first particle forming the torsion
particle2 – the index of the second particle forming the torsion
particle3 – the index of the third particle forming the torsion
particle4 – the index of the fourth particle forming the torsion
periodicity – the periodicity of the torsion
phase – the phase offset of the torsion, measured in radians
k – the force constant for the torsion

void updateParametersInContext(Context &context)¶
Update the pertorsion parameters in a Context to match those stored in this Force object. This method provides an efficient method to update certain parameters in an existing Context without needing to reinitialize it. Simply call setTorsionParameters() to modify this object’s parameters, then call updateParametersInContext() to copy them over to the Context.
The only information this method updates is the values of pertorsion parameters. The set of particles involved in a torsion cannot be changed, nor can new torsions be added.

void setUsesPeriodicBoundaryConditions(bool periodic)¶
Set whether this force should apply periodic boundary conditions when calculating displacements. Usually this is not appropriate for bonded forces, but there are situations when it can be useful.

virtual bool usesPeriodicBoundaryConditions() const¶
Returns whether or not this force makes use of periodic boundary conditions.
 Returns
true if force uses PBC and false otherwise

PeriodicTorsionForce()¶