# MonteCarloAnisotropicBarostat¶

class OpenMM::MonteCarloAnisotropicBarostat

This class uses a Monte Carlo algorithm to adjust the size of the periodic box, simulating the effect of constant pressure.

This class is similar to MonteCarloBarostat, but each Monte Carlo move is applied to only one axis of the periodic box (unlike MonteCarloBarostat, which scales the entire box isotropically). This means that the box may change shape as well as size over the course of the simulation. It also allows you to specify a different pressure for each axis of the box, or to keep the box size fixed along certain axes while still allowing it to change along others.

This class assumes the simulation is also being run at constant temperature, and requires you to specify the system temperature (since it affects the acceptance probability for Monte Carlo moves). It does not actually perform temperature regulation, however. You must use another mechanism along with it to maintain the temperature, such as LangevinIntegrator or AndersenThermostat.

Methods

 MonteCarloAnisotropicBarostat Create a MonteCarloAnisotropicBarostat. getDefaultPressure Get the default pressure (in bar). setDefaultPressure Set the default pressure acting on the system. getScaleX Get whether to allow the X dimension of the periodic box to change size. getScaleY Get whether to allow the Y dimension of the periodic box to change size. getScaleZ Get whether to allow the Z dimension of the periodic box to change size. getFrequency Get the frequency (in time steps) at which Monte Carlo pressure changes should be attempted. setFrequency Set the frequency (in time steps) at which Monte Carlo pressure changes should be attempted. getDefaultTemperature Get the default temperature at which the system is being maintained, measured in Kelvin. setDefaultTemperature Set the default temperature at which the system is being maintained. getRandomNumberSeed Get the random number seed. setRandomNumberSeed Set the random number seed. usesPeriodicBoundaryConditions Returns whether or not this force makes use of periodic boundary conditions.
const std::string &PressureX()

This is the name of the parameter which stores the current pressure acting on the X-axis (in bar).

const std::string &PressureY()

This is the name of the parameter which stores the current pressure acting on the Y-axis (in bar).

const std::string &PressureZ()

This is the name of the parameter which stores the current pressure acting on the Z-axis (in bar).

const std::string &Temperature()

This is the name of the parameter which stores the current temperature at which the system is being maintained (in Kelvin)

MonteCarloAnisotropicBarostat(const Vec3 &defaultPressure, double defaultTemperature, bool scaleX = true, bool scaleY = true, bool scaleZ = true, int frequency = 25)
• defaultPressure – The default pressure acting on each axis (in bar)
• defaultTemperature – the default temperature at which the system is being maintained (in Kelvin)
• scaleX – whether to allow the X dimension of the periodic box to change size
• scaleY – whether to allow the Y dimension of the periodic box to change size
• scaleZ – whether to allow the Z dimension of the periodic box to change size
• frequency – the frequency at which Monte Carlo pressure changes should be attempted (in time steps)
const Vec3 &getDefaultPressure() const

Get the default pressure (in bar).

Returns: the default pressure acting along each axis, measured in bar.
void setDefaultPressure(const Vec3 &pressure)

Set the default pressure acting on the system. This will affect any new Contexts you create, but not ones that already exist.

• pressure – the default pressure acting on the system, measured in bar.
bool getScaleX() const

Get whether to allow the X dimension of the periodic box to change size.

bool getScaleY() const

Get whether to allow the Y dimension of the periodic box to change size.

bool getScaleZ() const

Get whether to allow the Z dimension of the periodic box to change size.

int getFrequency() const

Get the frequency (in time steps) at which Monte Carlo pressure changes should be attempted. If this is set to 0, the barostat is disabled.

void setFrequency(int freq)

Set the frequency (in time steps) at which Monte Carlo pressure changes should be attempted. If this is set to 0, the barostat is disabled.

double getDefaultTemperature() const

Get the default temperature at which the system is being maintained, measured in Kelvin.

void setDefaultTemperature(double temp)

Set the default temperature at which the system is being maintained. This will affect any new Contexts you create, but not ones that already exist.

• temp – the system temperature, measured in Kelvin.
int getRandomNumberSeed() const

Get the random number seed. See setRandomNumberSeed() for details.

void setRandomNumberSeed(int seed)

Set the random number seed. It is guaranteed that if two simulations are run with different random number seeds, the sequence of Monte Carlo steps will be different. On the other hand, no guarantees are made about the behavior of simulations that use the same seed. In particular, Platforms are permitted to use non-deterministic algorithms which produce different results on successive runs, even if those runs were initialized identically.

If seed is set to 0 (which is the default value assigned), a unique seed is chosen when a Context is created from this Force. This is done to ensure that each Context receives unique random seeds without you needing to set them explicitly.

bool usesPeriodicBoundaryConditions() const

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

Returns: true if force uses PBC and false otherwise