DrudeLangevinIntegrator

class DrudeLangevinIntegrator : public OpenMM::DrudeIntegrator

This Integrator simulates systems that include Drude particles. It applies two different Langevin thermostats to different parts of the system. The first is applied to ordinary particles (ones that are not part of a Drude particle pair), as well as to the center of mass of each Drude particle pair. A second thermostat, typically with a much lower temperature, is applied to the relative internal displacement of each pair.

This integrator can optionally set an upper limit on how far any Drude particle is ever allowed to get from its parent particle. This can sometimes help to improve stability. The limit is enforced with a hard wall constraint. By default the limit is set to 0.02 nm.

This Integrator requires the System to include a DrudeForce, which it uses to identify the Drude particles.

Public Functions

DrudeLangevinIntegrator(double temperature, double frictionCoeff, double drudeTemperature, double drudeFrictionCoeff, double stepSize)

Create a DrudeLangevinIntegrator.

Parameters

  • temperature – the temperature of the main heat bath (in Kelvin)

  • frictionCoeff – the friction coefficient which couples the system to the main heat bath (in inverse picoseconds)

  • drudeTemperature – the temperature of the heat bath applied to internal coordinates of Drude particles (in Kelvin)

  • drudeFrictionCoeff – the friction coefficient which couples the system to the heat bath applied to internal coordinates of Drude particles (in inverse picoseconds)

  • stepSize – the step size with which to integrator the system (in picoseconds)

inline double getTemperature() const

Get the temperature of the main heat bath (in Kelvin).

Returns

the temperature of the heat bath, measured in Kelvin

void setTemperature(double temp)

Set the temperature of the main heat bath (in Kelvin).

Parameters

temp – the temperature of the heat bath, measured in Kelvin

inline double getFriction() const

Get the friction coefficient which determines how strongly the system is coupled to the main heat bath (in inverse ps).

Returns

the friction coefficient, measured in 1/ps

void setFriction(double coeff)

Set the friction coefficient which determines how strongly the system is coupled to the main heat bath (in inverse ps).

Parameters

coeff – the friction coefficient, measured in 1/ps

inline double getDrudeFriction() const

Get the friction coefficient which determines how strongly the internal coordinates of Drude particles are coupled to the heat bath (in inverse ps).

Returns

the friction coefficient, measured in 1/ps

void setDrudeFriction(double coeff)

Set the friction coefficient which determines how strongly the internal coordinates of Drude particles are coupled to the heat bath (in inverse ps).

Parameters

coeff – the friction coefficient, measured in 1/ps

virtual void step(int steps) override

Advance a simulation through time by taking a series of time steps.

Parameters

steps – the number of time steps to take

double computeSystemTemperature()

Compute the instantaneous temperature of the System, measured in Kelvin. This is calculated based on the kinetic energy of the ordinary particles (ones not attached to a Drude particle), as well as the center of mass motion of the Drude particle pairs. It does not include the internal motion of the pairs. On average, this should be approximately equal to the value returned by getTemperature().

double computeDrudeTemperature()

Compute the instantaneous temperature of the Drude system, measured in Kelvin. This is calculated based on the kinetic energy of the internal motion of Drude pairs and should remain close to the prescribed Drude temperature.