PeriodicTorsionForce¶

class
OpenMM::
PeriodicTorsionForce
¶ 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 calladdTorsion()
once for each torsion. After a torsion has been added, you can modify its force field parameters by callingsetTorsionParameters()
. This will have no effect on Contexts that already exist unless you callupdateParametersInContext()
.Methods
PeriodicTorsionForce
Create a PeriodicTorsionForce
.getNumTorsions
Get the number of periodic torsion terms in the potential function addTorsion
Add a periodic torsion term to the force field. getTorsionParameters
Get the force field parameters for a periodic torsion term. setTorsionParameters
Set the force field parameters for a periodic torsion term. updateParametersInContext
Update the pertorsion parameters in a Context
to match those stored in thisForce
object.setUsesPeriodicBoundaryConditions
Set whether this force should apply periodic boundary conditions when calculating displacements. usesPeriodicBoundaryConditions
Returns whether or not this force makes use of periodic boundary conditions. 
PeriodicTorsionForce
()¶ Create a
PeriodicTorsionForce()
.

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 thisForce
object. This method provides an efficient method to update certain parameters in an existingContext
without needing to reinitialize it. Simply callsetTorsionParameters()
to modify this object’s parameters, then callupdateParametersInContext()
to copy them over to theContext
.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.

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