openmmtools.testsystems.IdealGas

class openmmtools.testsystems.IdealGas(nparticles=216, mass=Quantity(value=39.9, unit=dalton), temperature=Quantity(value=298.0, unit=kelvin), pressure=Quantity(value=1.0, unit=atmosphere), volume=None, **kwargs)

Create an ‘ideal gas’ of noninteracting particles in a periodic box.

Parameters:

nparticles : int, optional, default=216

number of particles

mass : int, optional, default=39.9 * unit.amu

temperature : int, optional, default=298.0 * unit.kelvin

pressure : int, optional, default=1.0 * unit.atmosphere

volume : None

if None, defaults to (nparticles * temperature * unit.BOLTZMANN_CONSTANT_kB / pressure).in_units_of(unit.nanometers**3)

Examples

Create an ideal gas system.

>>> gas = IdealGas()
>>> system, positions = gas.system, gas.positions

Create a smaller ideal gas system containing 64 particles.

>>> gas = IdealGas(nparticles=64)
>>> system, positions = gas.system, gas.positions

Attributes:

analytical_properties

A list of available analytical properties, accessible via ‘get_propertyname(thermodynamic_state)’ calls.

mdtraj_topology

The mdtraj.Topology object corresponding to the test system (read-only).

name

The name of the test system.

positions

The simtk.unit.Quantity object containing the particle positions, with units compatible with simtk.unit.nanometers.

system

The simtk.openmm.System object corresponding to the test system.

topology

The simtk.openmm.app.Topology object corresponding to the test system.

Methods

get_kinetic_expectation(state)	Return the expectation of the kinetic energy, computed analytically or numerically.
get_kinetic_standard_deviation(state)	Return the standard deviation of the kinetic energy, computed analytically or numerically.
get_potential_expectation(state)	Return the expectation of the potential energy, computed analytically or numerically.
get_potential_standard_deviation(state)	Return the standard deviation of the potential energy, computed analytically or numerically.
get_volume_expectation(state)	Return the expectation of the volume, computed analytically.
get_volume_standard_deviation(state)	Return the standard deviation of the volume, computed analytically.
reduced_potential_expectation(…)	Calculate the expected potential energy in state_sampled_from, divided by kB * T in state_evaluated_in.
serialize()	Return the System and positions in serialized XML form.

__init__(nparticles=216, mass=Quantity(value=39.9, unit=dalton), temperature=Quantity(value=298.0, unit=kelvin), pressure=Quantity(value=1.0, unit=atmosphere), volume=None, **kwargs)

Abstract base class for test system.

Methods

__init__([nparticles, mass, unit, …])	Abstract base class for test system.
get_kinetic_expectation(state)	Return the expectation of the kinetic energy, computed analytically or numerically.
get_kinetic_standard_deviation(state)	Return the standard deviation of the kinetic energy, computed analytically or numerically.
get_potential_expectation(state)	Return the expectation of the potential energy, computed analytically or numerically.
get_potential_standard_deviation(state)	Return the standard deviation of the potential energy, computed analytically or numerically.
get_volume_expectation(state)	Return the expectation of the volume, computed analytically.
get_volume_standard_deviation(state)	Return the standard deviation of the volume, computed analytically.
reduced_potential_expectation(…)	Calculate the expected potential energy in state_sampled_from, divided by kB * T in state_evaluated_in.
serialize()	Return the System and positions in serialized XML form.

Attributes

analytical_properties	A list of available analytical properties, accessible via ‘get_propertyname(thermodynamic_state)’ calls.
mdtraj_topology	The mdtraj.Topology object corresponding to the test system (read-only).
name	The name of the test system.
positions	The simtk.unit.Quantity object containing the particle positions, with units compatible with simtk.unit.nanometers.
system	The simtk.openmm.System object corresponding to the test system.
topology	The simtk.openmm.app.Topology object corresponding to the test system.

analytical_properties

A list of available analytical properties, accessible via ‘get_propertyname(thermodynamic_state)’ calls.

get_kinetic_expectation(state)

Return the expectation of the kinetic energy, computed analytically or numerically.

Parameters:

state : ThermodynamicState with temperature defined

The thermodynamic state at which the property is to be computed.

Returns:

potential_mean : simtk.unit.Quantity compatible with simtk.unit.kilojoules_per_mole

The expectation of the potential energy.

get_kinetic_standard_deviation(state)

Return the standard deviation of the kinetic energy, computed analytically or numerically.

Parameters:

state : ThermodynamicState with temperature defined

The thermodynamic state at which the property is to be computed.

Returns:

potential_stddev : simtk.unit.Quantity compatible with simtk.unit.kilojoules_per_mole

potential energy standard deviation if implemented, or else None

get_potential_expectation(state)

Return the expectation of the potential energy, computed analytically or numerically.

Parameters:

state : ThermodynamicState with temperature defined

The thermodynamic state at which the property is to be computed.

Returns:

potential_mean : simtk.unit.Quantity compatible with simtk.unit.kilojoules_per_mole

The expectation of the potential energy.

get_potential_standard_deviation(state)

Return the standard deviation of the potential energy, computed analytically or numerically.

Parameters:

state : ThermodynamicState with temperature defined

The thermodynamic state at which the property is to be computed.

Returns:

potential_stddev : simtk.unit.Quantity compatible with simtk.unit.kilojoules_per_mole

potential energy standard deviation if implemented, or else None

get_volume_expectation(state)

Return the expectation of the volume, computed analytically.

Parameters:

state : ThermodynamicState with temperature and pressure defined

The thermodynamic state at which the property is to be computed.

Returns:

volume_mean : simtk.unit.Quantity compatible with simtk.unit.nanometers**3

The expectation of the volume at equilibrium.

Notes

The true mean volume is used, rather than the large-N limit.

get_volume_standard_deviation(state)

Return the standard deviation of the volume, computed analytically.

Parameters:

state : ThermodynamicState with temperature and pressure defined

The thermodynamic state at which the property is to be computed.

Returns:

volume_stddev : simtk.unit.Quantity compatible with simtk.unit.nanometers**3

The standard deviation of the volume at equilibrium.

Notes

The true mean volume is used, rather than the large-N limit.

mdtraj_topology

The mdtraj.Topology object corresponding to the test system (read-only).

name

The name of the test system.

positions

The simtk.unit.Quantity object containing the particle positions, with units compatible with simtk.unit.nanometers.

reduced_potential_expectation(state_sampled_from, state_evaluated_in)

Calculate the expected potential energy in state_sampled_from, divided by kB * T in state_evaluated_in.

Notes

This is not called get_reduced_potential_expectation because this function requires two, not one, inputs.

serialize()

Return the System and positions in serialized XML form.

Returns:

system_xml : str

Serialized XML form of System object.

state_xml : str

Serialized XML form of State object containing particle positions.

system

The simtk.openmm.System object corresponding to the test system.

topology

The simtk.openmm.app.Topology object corresponding to the test system.