# PeriodicTorsionForce¶

class simtk.openmm.openmm.PeriodicTorsionForce(*args)

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().

__init__(self) → PeriodicTorsionForce

__init__(self, other) -> PeriodicTorsionForce

Create a PeriodicTorsionForce.

Methods

 __init__((self) -> PeriodicTorsionForce) __init__(self, other) -> PeriodicTorsionForce addTorsion((self, particle1, particle2, ...) Add a periodic torsion term to the force field. getForceGroup((self) -> int) Get the force group this Force belongs to. getNumTorsions((self) -> int) Get the number of periodic torsion terms in the potential function getTorsionParameters(self, index) Get the force field parameters for a periodic torsion term. setForceGroup(self, group) Set the force group this Force belongs to. setTorsionParameters(self, index, particle1, ...) Set the force field parameters for a periodic torsion term. setUsesPeriodicBoundaryConditions(self, periodic) Set whether this force should apply periodic boundary conditions when calculating displacements. updateParametersInContext(self, context) Update the per-torsion parameters in a Context to match those stored in this Force object. usesPeriodicBoundaryConditions((self) -> bool) Returns whether or not this force makes use of periodic boundary conditions.
getNumTorsions(self) → int

Get the number of periodic torsion terms in the potential function

addTorsion(self, particle1, particle2, particle3, particle4, periodicity, phase, k) → int

Add a periodic torsion term to the force field.

Parameters: particle1 (int) – the index of the first particle forming the torsion particle2 (int) – the index of the second particle forming the torsion particle3 (int) – the index of the third particle forming the torsion particle4 (int) – the index of the fourth particle forming the torsion periodicity (int) – the periodicity of the torsion phase (double) – the phase offset of the torsion, measured in radians k (double) – the force constant for the torsion the index of the torsion that was added int
getTorsionParameters(self, index)

Get the force field parameters for a periodic torsion term.

Parameters: index (int) – the index of the torsion for which to get parameters particle1 (int) – the index of the first particle forming the torsion particle2 (int) – the index of the second particle forming the torsion particle3 (int) – the index of the third particle forming the torsion particle4 (int) – the index of the fourth particle forming the torsion periodicity (int) – the periodicity of the torsion phase (double) – the phase offset of the torsion, measured in radians k (double) – the force constant for the torsion
setTorsionParameters(self, index, particle1, particle2, particle3, particle4, periodicity, phase, k)

Set the force field parameters for a periodic torsion term.

Parameters: index (int) – the index of the torsion for which to set parameters particle1 (int) – the index of the first particle forming the torsion particle2 (int) – the index of the second particle forming the torsion particle3 (int) – the index of the third particle forming the torsion particle4 (int) – the index of the fourth particle forming the torsion periodicity (int) – the periodicity of the torsion phase (double) – the phase offset of the torsion, measured in radians k (double) – the force constant for the torsion
updateParametersInContext(self, context)

Update the per-torsion 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 per-torsion parameters. The set of particles involved in a torsion cannot be changed, nor can new torsions be added.

setUsesPeriodicBoundaryConditions(self, 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.

usesPeriodicBoundaryConditions(self) → bool

Returns whether or not this force makes use of periodic boundary conditions.

Returns: true if force uses PBC and false otherwise bool
__copy__(self) → Force
getForceGroup(self) → int

Get the force group this Force belongs to.

setForceGroup(self, group)

Set the force group this Force belongs to.

Parameters: group (int) – the group index. Legal values are between 0 and 31 (inclusive).