Action: ECV_MULTITHERMAL_MULTIBARIC

Module	opes
Description	Usage
Expand a simulation to sample multiple temperatures and pressures.

Details and examples

Expand a simulation to sample multiple temperatures and pressures.

The potential ENERGY, $E$ , and the VOLUME, $V$ , of the system should be used as ARG.

$\Delta u_{\beta',p'}=(\beta'-\beta) E + (\beta' p' -\beta p) V\, ,$

where $\beta', p'$ are the temperatures and pressures to be sampled, while $\beta, p$ is the temperature and pressure at which the simulation is conducted.

If instead you wish to sample multiple temperatures and a single pressure, you should use ECV_MULTITHERMAL with as ARG the internal energy $U=E+pV$ .

The TEMP_STEPS and PRESSURE_STEPS are automatically guessed from the initial unbiased steps (see OBSERVATION_STEPS in OPES_EXPANDED), unless explicitly set. The algorithm for this guess is described in the paper cited below should provide a rough estimate useful for most applications. The pressures are uniformely spaced, while the temperatures steps are geometrically spaced. Use instead the keyword NO_GEOM_SPACING for a linear spacing in inverse temperature (beta). For more detailed control you can use instead TEMP_SET_ALL and/or PRESSURE_SET_ALL to explicitly set all of them. The temperatures and pressures are then combined in a 2D grid.

You can use CUT_CORNER to avoid a high-temperature/low-pressure region. This can be useful e.g. to increase the temperature for greater ergodicity, while avoiding water to vaporize, as in the paper cited below.

You can reweight the resulting simulation at any temperature and pressure in chosen target, using e.g. REWEIGHT_TEMP_PRESS. A similar target distribution can be sampled using TD_MULTITHERMAL_MULTIBARIC](TD_MULTITHERMAL_MULTIBARIC.md).

Examples

Click on the labels of the actions for more information on what each action computes

eneThe ENERGY action with label ene calculates the following quantities: Quantity    Type    Description  
ene scalar the internal energy: ENERGYCalculate the total potential energy of the simulation box. More details
volThe VOLUME action with label vol calculates the following quantities: Quantity    Type    Description  
vol scalar the volume of simulation box: VOLUMECalculate the volume the simulation box. More details
ecvThe ECV_MULTITHERMAL_MULTIBARIC action with label ecv calculates the following quantities: Quantity    Type    Description  
ecv.ene scalar the value of the argument named ene
ecv.vol scalar the value of the argument named vol: ECV_MULTITHERMAL_MULTIBARICExpand a simulation to sample multiple temperatures and pressures. More details ...
  ARGthe labels of the potential energy and of the volume of the system=ene,vol
  TEMP temperature=500
  TEMP_MINthe minimum of the temperature range=270
  TEMP_MAXthe maximum of the temperature range=800
  PRESSUREpressure=0.06022140857*2000 #2 kbar
  PRESSURE_MINthe minimum of the pressure range=0.06022140857  #1 bar
  PRESSURE_MAXthe maximum of the pressure range=0.06022140857*4000 #4 kbar
  CUT_CORNERavoid region of high temperature and low pressure=500,0.06022140857,800,0.06022140857*1000
...
opesThe OPES_EXPANDED action with label opes calculates the following quantities: Quantity    Type    Description  
opes.bias scalar the instantaneous value of the bias potential: OPES_EXPANDEDOn-the-fly probability enhanced sampling with expanded ensembles for the target distribution. This action has hidden defaults. More details ARGthe label of the ECVs that define the expansion=ecv.* FILE a file with the estimate of the relative Delta F for each component of the target and of the global c(t)=DeltaF.data PACEhow often the bias is updated=500 WALKERS_MPI switch on MPI version of multiple walkers
opes: OPES_EXPANDEDOn-the-fly probability enhanced sampling with expanded ensembles for the target distribution. This action uses the defaults shown here. More details ARGthe label of the ECVs that define the expansion=ecv.* FILE a file with the estimate of the relative Delta F for each component of the target and of the global c(t)=DeltaF.data PACEhow often the bias is updated=500 WALKERS_MPI switch on MPI version of multiple walkers  OBSERVATION_STEPS number of unbiased initial PACE steps to collect statistics for initialization=100 PRINT_STRIDE stride for printing to DELTAFS file, in units of PACE=100

Notice that $p=0.06022140857$ corresponds to 1 bar only when using the default PLUMED units. If you modify them via the UNITS command, then the pressure has to be rescaled accordingly.

Input

The arguments that serve as the input for this action are specified using one or more of the keywords in the following table.

Keyword	Type	Description
ARG	scalar	the labels of the potential energy and of the volume of the system

Full list of keywords

The following table describes the keywords and options that can be used with this action

Keyword	Type	Default	Description
ARG	input	none	the labels of the potential energy and of the volume of the system
TEMP	compulsory	-1	temperature
PRESSURE	compulsory	none	pressure
NUMERICAL_DERIVATIVESThis keyword do not have examples	optional	false	calculate the derivatives for these quantities numerically
TEMP_MIN	optional	not used	the minimum of the temperature range
TEMP_MAX	optional	not used	the maximum of the temperature range
TEMP_STEPSThis keyword do not have examples	optional	not used	the number of steps in temperature
TEMP_SET_ALLThis keyword do not have examples	optional	not used	manually set all the temperatures
NO_GEOM_SPACINGThis keyword do not have examples	optional	false	do not use geometrical spacing in temperature, but instead linear spacing in inverse temperature
PRESSURE_MIN	optional	not used	the minimum of the pressure range
PRESSURE_MAX	optional	not used	the maximum of the pressure range
PRESSURE_STEPSThis keyword do not have examples	optional	not used	the number of steps in pressure
PRESSURE_SET_ALLThis keyword do not have examples	optional	not used	manually set all the pressures
SET_ALL_TEMP_PRESSUREThis keyword do not have examples	optional	not used	manually set all the target temperature_pressure pairs
CUT_CORNER	optional	not used	avoid region of high temperature and low pressure

References

More information about how this action can be used is available in the following articles:

M. Invernizzi, P. M. Piaggi, M. Parrinello, Unified Approach to Enhanced Sampling. Physical Review X. 10 (2020)

Quantity	Type	Description
ene	scalar	the internal energy