HippoNonbondedForce
¶

class HippoNonbondedForce : public OpenMM::Force¶
This class implements all nonbonded interactions in the HIPPO force field: electrostatics, induction, charge transfer, dispersion, and repulsion. Although some of these are conceptually distinct, they share parameters in common and are most efficiently computed together. For example, the same multipole definitions are used for both electrostatics and Pauli repulsion. Therefore, all of them are computed by a single Force object.
To use it, create a HippoNonbondedForce object, then call addParticle() once for each particle. After an entry has been added, you can modify its force field parameters by calling setParticleParameters(). This will have no effect on Contexts that already exist unless you call updateParametersInContext().
You also can specify “exceptions”, particular pairs of particles whose interactions should be reduced or completely omitted. Call addException() to define exceptions.
Public Functions

HippoNonbondedForce()¶
Create a HippoNonbondedForce.

inline int getNumParticles() const¶
Get the number of particles in the potential function.

inline int getNumExceptions() const¶
Get the number of exceptions.

NonbondedMethod getNonbondedMethod() const¶
Get the method used for handling longrange nonbonded interactions.

void setNonbondedMethod(NonbondedMethod method)¶
Set the method used for handling longrange nonbonded interactions.

double getCutoffDistance() const¶
Get the cutoff distance (in nm) being used for nonbonded interactions. If the NonbondedMethod in use is NoCutoff, this value will have no effect.
 Returns
the cutoff distance, measured in nm

void setCutoffDistance(double distance)¶
Set the cutoff distance (in nm) being used for nonbonded interactions. If the NonbondedMethod in use is NoCutoff, this value will have no effect.
 Parameters
distance – the cutoff distance, measured in nm

double getSwitchingDistance() const¶
Get the distance at which the switching function begins to reduce the repulsion and charge transfer interactions. This must be less than the cutoff distance.

void setSwitchingDistance(double distance)¶
Set the distance at which the switching function begins to reduce the repulsion and charge transfer interactions. This must be less than the cutoff distance.

const std::vector<double> &getExtrapolationCoefficients() const¶
Get the coefficients for the mu_0, mu_1, mu_2, …, mu_n terms in the extrapolation algorithm for induced dipoles.

void setExtrapolationCoefficients(const std::vector<double> &coefficients)¶
Set the coefficients for the mu_0, mu_1, mu_2, …, mu_n terms in the extrapolation algorithm for induced dipoles.
 Parameters
coefficients – a vector whose mth entry specifies the coefficient for mu_m. The length of this vector determines how many iterations are performed.

void getPMEParameters(double &alpha, int &nx, int &ny, int &nz) const¶
Get the parameters to use for PME calculations. If alpha is 0 (the default), these parameters are ignored and instead their values are chosen based on the Ewald error tolerance.
 Parameters
alpha – [out] the separation parameter
nx – [out] the number of grid points along the X axis
ny – [out] the number of grid points along the Y axis
nz – [out] the number of grid points along the Z axis

void getDPMEParameters(double &alpha, int &nx, int &ny, int &nz) const¶
Get the parameters to use for dispersion PME calculations. If alpha is 0 (the default), these parameters are ignored and instead their values are chosen based on the Ewald error tolerance.
 Parameters
alpha – [out] the separation parameter
nx – [out] the number of dispersion grid points along the X axis
ny – [out] the number of dispersion grid points along the Y axis
nz – [out] the number of dispersion grid points along the Z axis

void setPMEParameters(double alpha, int nx, int ny, int nz)¶
Set the parameters to use for PME calculations. If alpha is 0 (the default), these parameters are ignored and instead their values are chosen based on the Ewald error tolerance.
 Parameters
alpha – the separation parameter
nx – the number of grid points along the X axis
ny – the number of grid points along the Y axis
nz – the number of grid points along the Z axis

void setDPMEParameters(double alpha, int nx, int ny, int nz)¶
Set the parameters to use for dispersion PME calculations. If alpha is 0 (the default), these parameters are ignored and instead their values are chosen based on the Ewald error tolerance.
 Parameters
alpha – the separation parameter
nx – the number of grid points along the X axis
ny – the number of grid points along the Y axis
nz – the number of grid points along the Z axis

void getPMEParametersInContext(const Context &context, double &alpha, int &nx, int &ny, int &nz) const¶
Get the parameters being used for PME in a particular Context. Because some platforms have restrictions on the allowed grid sizes, the values that are actually used may be slightly different from those specified with setPmeGridDimensions(), or the standard values calculated based on the Ewald error tolerance. See the manual for details.
 Parameters
context – the Context for which to get the parameters
alpha – [out] the separation parameter
nx – [out] the number of grid points along the X axis
ny – [out] the number of grid points along the Y axis
nz – [out] the number of grid points along the Z axis

void getDPMEParametersInContext(const Context &context, double &alpha, int &nx, int &ny, int &nz) const¶
Get the parameters being used for dispersion PME in a particular Context. Because some platforms have restrictions on the allowed grid sizes, the values that are actually used may be slightly different from those specified with setPMEParameters(), or the standard values calculated based on the Ewald error tolerance. See the manual for details.
 Parameters
context – the Context for which to get the parameters
alpha – [out] the separation parameter
nx – [out] the number of grid points along the X axis
ny – [out] the number of grid points along the Y axis
nz – [out] the number of grid points along the Z axis

int addParticle(double charge, const std::vector<double> &dipole, const std::vector<double> &quadrupole, double coreCharge, double alpha, double epsilon, double damping, double c6, double pauliK, double pauliQ, double pauliAlpha, double polarizability, int axisType, int multipoleAtomZ, int multipoleAtomX, int multipoleAtomY)¶
Add the nonbonded force parameters for a particle. This should be called once for each particle in the System. When it is called for the i’th time, it specifies the parameters for the i’th particle.
 Parameters
charge – the particle’s charge
dipole – the particle’s molecular dipole (vector of size 3)
quadrupole – the particle’s molecular quadrupole (vector of size 9)
coreCharge – the charge of the atomic core
alpha – controls the width of the particle’s electron density
epsilon – sets the magnitude of charge transfer
damping – sets the length scale for charge transfer
c6 – the coefficient of the dispersion interaction
pauliK – the coefficient of the Pauli repulsion interaction
pauliQ – the charge used in computing the Pauli repulsion interaction
pauliAlpha – the width of the particle’s electron density for computing the Pauli repulsion interaction
polarizability – atomic polarizability
axisType – the particle’s axis type
multipoleAtomZ – index of first atom used in defining the local coordinate system for multipoles
multipoleAtomX – index of second atom used in defining the local coordinate system for multipoles
multipoleAtomY – index of third atom used in defining the local coordinate system for multipoles
 Returns
the index of the particle that was added

void getParticleParameters(int index, double &charge, std::vector<double> &dipole, std::vector<double> &quadrupole, double &coreCharge, double &alpha, double &epsilon, double &damping, double &c6, double &pauliK, double &pauliQ, double &pauliAlpha, double &polarizability, int &axisType, int &multipoleAtomZ, int &multipoleAtomX, int &multipoleAtomY) const¶
Get the nonbonded force parameters for a particle.
 Parameters
index – the index of the particle for which to get parameters
charge – the particle’s charge
dipole – the particle’s molecular dipole (vector of size 3)
quadrupole – the particle’s molecular quadrupole (vector of size 9)
coreCharge – the charge of the atomic core
alpha – controls the width of the particle’s electron density
epsilon – sets the magnitude of charge transfer
damping – sets the length scale for charge transfer
c6 – the coefficient of the dispersion interaction
pauliK – the coefficient of the Pauli repulsion interaction
pauliQ – the charge used in computing the Pauli repulsion interaction
pauliAlpha – the width of the particle’s electron density for computing the Pauli repulsion interaction
polarizability – atomic polarizability
axisType – the particle’s axis type
multipoleAtomZ – index of first atom used in defining the local coordinate system for multipoles
multipoleAtomX – index of second atom used in defining the local coordinate system for multipoles
multipoleAtomY – index of third atom used in defining the local coordinate system for multipoles

void setParticleParameters(int index, double charge, const std::vector<double> &dipole, const std::vector<double> &quadrupole, double coreCharge, double alpha, double epsilon, double damping, double c6, double pauliK, double pauliQ, double pauliAlpha, double polarizability, int axisType, int multipoleAtomZ, int multipoleAtomX, int multipoleAtomY)¶
Set the nonbonded force parameters for a particle.
 Parameters
index – the index of the particle for which to set parameters
charge – the particle’s charge
dipole – the particle’s molecular dipole (vector of size 3)
quadrupole – the particle’s molecular quadrupole (vector of size 9)
coreCharge – the charge of the atomic core
alpha – controls the width of the particle’s electron density
epsilon – sets the magnitude of charge transfer
damping – sets the length scale for charge transfer
c6 – the coefficient of the dispersion interaction
pauliK – the coefficient of the Pauli repulsion interaction
pauliQ – the charge used in computing the Pauli repulsion interaction
pauliAlpha – the width of the particle’s electron density for computing the Pauli repulsion interaction
polarizability – atomic polarizability
axisType – the particle’s axis type
multipoleAtomZ – index of first atom used in defining the local coordinate system for multipoles
multipoleAtomX – index of second atom used in defining the local coordinate system for multipoles
multipoleAtomY – index of third atom used in defining the local coordinate system for multipoles

int addException(int particle1, int particle2, double multipoleMultipoleScale, double dipoleMultipoleScale, double dipoleDipoleScale, double dispersionScale, double repulsionScale, double chargeTransferScale, bool replace = false)¶
Add an interaction to the list of exceptions that should be calculated differently from other interactions. If all scale factors are set to 0, this will cause the interaction to be completely omitted from force and energy calculations.
 Parameters
particle1 – the index of the first particle involved in the interaction
particle2 – the index of the second particle involved in the interaction
multipoleMultipoleScale – the factor by which to scale the Coulomb interaction between fixed multipoles
dipoleMultipoleScale – the factor by which to scale the Coulomb interaction between an induced dipole and a fixed multipole
dipoleDipoleScale – the factor by which to scale the Coulomb interaction between induced dipoles
dispersionScale – the factor by which to scale the dispersion interaction
repulsionScale – the factor by which to scale the Pauli repulsion
chargeTransferScale – the factor by which to scale the charge transfer interaction
replace – determines the behavior if there is already an exception for the same two particles. If true, the existing one is replaced. If false, an exception is thrown.
 Returns
the index of the exception that was added

void getExceptionParameters(int index, int &particle1, int &particle2, double &multipoleMultipoleScale, double &dipoleMultipoleScale, double &dipoleDipoleScale, double &dispersionScale, double &repulsionScale, double &chargeTransferScale) const¶
Get the scale factors for an interaction that should be calculated differently from others.
 Parameters
index – the index of the interaction for which to get parameters
particle1 – the index of the first particle involved in the interaction
particle2 – the index of the second particle involved in the interaction
multipoleMultipoleScale – the factor by which to scale the Coulomb interaction between fixed multipoles
dipoleMultipoleScale – the factor by which to scale the Coulomb interaction between an induced dipole and a fixed multipole
dipoleDipoleScale – the factor by which to scale the Coulomb interaction between induced dipoles
dispersionScale – the factor by which to scale the dispersion interaction
repulsionScale – the factor by which to scale the Pauli repulsion
chargeTransferScale – the factor by which to scale the charge transfer interaction

void setExceptionParameters(int index, int particle1, int particle2, double multipoleMultipoleScale, double dipoleMultipoleScale, double dipoleDipoleScale, double dispersionScale, double repulsionScale, double chargeTransferScale)¶
Set the scale factors for an interaction that should be calculated differently from others. If all scale factors are set to 0, this will cause the interaction to be completely omitted from force and energy calculations.
 Parameters
index – the index of the interaction for which to set parameters
particle1 – the index of the first particle involved in the interaction
particle2 – the index of the second particle involved in the interaction
multipoleMultipoleScale – the factor by which to scale the Coulomb interaction between fixed multipoles
dipoleMultipoleScale – the factor by which to scale the Coulomb interaction between an induced dipole and a fixed multipole
dipoleDipoleScale – the factor by which to scale the Coulomb interaction between induced dipoles
dispersionScale – the factor by which to scale the dispersion interaction
repulsionScale – the factor by which to scale the Pauli repulsion
chargeTransferScale – the factor by which to scale the charge transfer interaction

double getEwaldErrorTolerance() const¶
Get the error tolerance for Ewald summation. This corresponds to the fractional error in the forces which is acceptable. This value is used to select the grid dimensions and separation (alpha) parameter so that the average error level will be less than the tolerance. There is not a rigorous guarantee that all forces on all atoms will be less than the tolerance, however.
This can be overridden by explicitly setting an alpha parameter and grid dimensions to use.

void setEwaldErrorTolerance(double tol)¶
Get the error tolerance for Ewald summation. This corresponds to the fractional error in the forces which is acceptable. This value is used to select the grid dimensions and separation (alpha) parameter so that the average error level will be less than the tolerance. There is not a rigorous guarantee that all forces on all atoms will be less than the tolerance, however.
This can be overridden by explicitly setting an alpha parameter and grid dimensions to use.

void getLabFramePermanentDipoles(Context &context, std::vector<Vec3> &dipoles)¶
Get the fixed dipole moments of all particles in the global reference frame.
 Parameters
context – the Context for which to get the fixed dipoles
dipoles – [out] the fixed dipole moment of particle i is stored into the i’th element

void getInducedDipoles(Context &context, std::vector<Vec3> &dipoles)¶
Get the induced dipole moments of all particles.
 Parameters
context – the Context for which to get the induced dipoles
dipoles – [out] the induced dipole moment of particle i is stored into the i’th element

void updateParametersInContext(Context &context)¶
Update the particle and exception 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 setParticleParameters() to modify this object’s parameters, then call updateParametersInContext() to copy them over to the Context.
This method has several limitations. The only information it updates is the parameters of particles and exceptions. All other aspects of the Force (the nonbonded method, the cutoff distance, etc.) are unaffected and can only be changed by reinitializing the Context. Furthermore, only the scale factors for an exception can be changed; the pair of particles involved in the exception cannot change. Finally, this method cannot be used to add new particles or exceptions, only to change the parameters of existing ones.

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

HippoNonbondedForce()¶