VariableLangevinIntegrator¶

class
OpenMM::
VariableLangevinIntegrator
¶ This is an error contolled, variable time step
Integrator
that simulates aSystem
using Langevin dynamics. It compares the result of the Langevin integrator to that of an explicit Euler integrator, takes the difference between the two as a measure of the integration error in each time step, and continuously adjusts the step size to keep the error below a specified tolerance. This both improves the stability of the integrator and allows it to take larger steps on average, while still maintaining comparable accuracy to a fixed step size integrator.It is best not to think of the error tolerance as having any absolute meaning. It is just an adjustable parameter that affects the step size and integration accuracy. You should try different values to find the largest one that produces a trajectory sufficiently accurate for your purposes. 0.001 is often a good starting point.
Methods
VariableLangevinIntegrator
Create a VariableLangevinIntegrator
.getTemperature
Get the temperature of the heat bath (in Kelvin). setTemperature
Set the temperature of the heat bath (in Kelvin). getFriction
Get the friction coefficient which determines how strongly the system is coupled to the heat bath (in inverse ps). setFriction
Set the friction coefficient which determines how strongly the system is coupled to the heat bath (in inverse ps). getErrorTolerance
Get the error tolerance. setErrorTolerance
Set the error tolerance. getRandomNumberSeed
Get the random number seed. setRandomNumberSeed
Set the random number seed. step
Advance a simulation through time by taking a series of time steps. stepTo
Advance a simulation through time by taking a series of steps until a specified time is reached. 
VariableLangevinIntegrator
(double temperature, double frictionCoeff, double errorTol)¶ Create a
VariableLangevinIntegrator()
.Parameters:  temperature – the temperature of the heat bath (in Kelvin)
 frictionCoeff – the friction coefficient which couples the system to the heat bath (in inverse picoseconds)
 errorTol – the error tolerance

double
getTemperature
() const¶ Get the temperature of the heat bath (in Kelvin).
Returns: the temperature of the heat bath, measured in Kelvin

void
setTemperature
(double temp)¶ Set the temperature of the heat bath (in Kelvin).
Parameters:  temp – the temperature of the heat bath, measured in Kelvin

double
getFriction
() const¶ Get the friction coefficient which determines how strongly the system is coupled to the 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 heat bath (in inverse ps).
Parameters:  coeff – the friction coefficient, measured in 1/ps

double
getErrorTolerance
() const¶ Get the error tolerance.

void
setErrorTolerance
(double tol)¶ Set the error tolerance.

int
getRandomNumberSeed
() const¶ Get the random number seed. See
setRandomNumberSeed()
for details.

void
setRandomNumberSeed
(int seed)¶ Set the random number seed. The precise meaning of this parameter is undefined, and is left up to each
Platform
to interpret in an appropriate way. It is guaranteed that if two simulations are run with different random number seeds, the sequence of random forces 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 nondeterministic 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 thisForce
. This is done to ensure that eachContext
receives unique random seeds without you needing to set them explicitly.

void
step
(int steps)¶ Advance a simulation through time by taking a series of time steps.
Parameters:  steps – the number of time steps to take

void
stepTo
(double time)¶ Advance a simulation through time by taking a series of steps until a specified time is reached. When this method returns, the simulation time will exactly equal the time which was specified. If you call this method and specify a time that is earlier than the current time, it will return without doing anything.
Parameters:  time – the time to which the simulation should be advanced
