# HarmonicAngleForce¶

class OpenMM::HarmonicAngleForce

This class implements an interaction between groups of three particles that varies harmonically with the angle between them. To use it, create a HarmonicAngleForce() object then call addAngle() once for each angle. After an angle has been added, you can modify its force field parameters by calling setAngleParameters(). This will have no effect on Contexts that already exist unless you call updateParametersInContext().

Methods

 HarmonicAngleForce() Create a HarmonicAngleForce(). getNumAngles() Get the number of harmonic bond angle terms in the potential function addAngle() Add an angle term to the force field. getAngleParameters() Get the force field parameters for an angle term. setAngleParameters() Set the force field parameters for an angle term. updateParametersInContext() Update the per-angle parameters in a Context to match those stored in this Force object. usesPeriodicBoundaryConditions() Returns whether or not this force makes use of periodic boundary conditions.
HarmonicAngleForce()

Create a HarmonicAngleForce().

int getNumAngles() const

Get the number of harmonic bond angle terms in the potential function

int addAngle(int particle1, int particle2, int particle3, double angle, double k)

Add an angle term to the force field.

• particle1 – the index of the first particle forming the angle
• particle2 – the index of the second particle forming the angle
• particle3 – the index of the third particle forming the angle
• angle – the equilibrium angle, measured in radians
• k – the harmonic force constant for the angle, measured in kJ/mol/radian^2
Returns: the index of the angle that was added
void getAngleParameters(int index, int &particle1, int &particle2, int &particle3, double &angle, double &k) const

Get the force field parameters for an angle term.

• index – the index of the angle for which to get parameters
• particle1 – [out] the index of the first particle forming the angle
• particle2 – [out] the index of the second particle forming the angle
• particle3 – [out] the index of the third particle forming the angle
• angle – [out] the equilibrium angle, measured in radians
• k – [out] the harmonic force constant for the angle, measured in kJ/mol/radian^2
void setAngleParameters(int index, int particle1, int particle2, int particle3, double angle, double k)

Set the force field parameters for an angle term.

• index – the index of the angle for which to set parameters
• particle1 – the index of the first particle forming the angle
• particle2 – the index of the second particle forming the angle
• particle3 – the index of the third particle forming the angle
• angle – the equilibrium angle, measured in radians
• k – the harmonic force constant for the angle, measured in kJ/mol/radian^2
void updateParametersInContext(Context &context)

Update the per-angle 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 setAngleParameters() 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-angle parameters. The set of particles involved in a angle cannot be changed, nor can new angles be added.

bool usesPeriodicBoundaryConditions() const

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

Returns: true if force uses PBC and false otherwise