Action: ECV_MULTITHERMAL

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

Details and examples

Expand a simulation to sample multiple temperatures simultaneously.

The internal energy $U$ of of the system should be used as ARG.

$$\Delta u_{\beta'}=(\beta'-\beta) U\, ,$$

where $\beta'$ are the temperatures to be sampled and $\beta$ is the temperature at which the simulation is conducted. In case of fixed volume, the internal energy is simply the potential energy given by the ENERGY colvar $U=E$, and you will run a multicanonical simulation. If instead the simulation is at fixed pressure $p$, the contribution of the volume must be added $U=E+pV$ (see example below).

By defauly the needed steps in temperatures are automatically guessed from few initial unbiased MD steps, as descibed in the paper cited below. Otherwise you can manually set this number with TEMP_STEPS. In both cases the steps will be geometrically spaced in temperature. Use instead the keyword NO_GEOM_SPACING for a linear spacing in the inverse temperature (beta), that typically increases the focus on lower temperatures. Finally, you can use instead the keyword TEMP_SET_ALL and explicitly provide each temperature.

You can reweight the resulting simulation at any temperature in the chosen range, using e.g. REWEIGHT_TEMP_PRESS. A similar target distribution can be sampled using TD_MULTICANONICAL.

Examples

Fixed volume, multicanonical simulation:

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
ecvThe ECV_MULTITHERMAL action with label ecv calculates the following quantities:
 Quantity   
 Type   
 Description  
ecv.ene
scalar
the value of the argument named ene: ECV_MULTITHERMALExpand a simulation to sample multiple temperatures simultaneously. More details ARGthe label of the internal energy of the system=ene TEMP temperature=300 TEMP_MINthe minimum of the temperature range=300 TEMP_MAXthe maximum of the temperature range=800
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.ene PACEhow often the bias is updated=500
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.ene PACEhow often the bias is updated=500  OBSERVATION_STEPS number of unbiased initial PACE steps to collect statistics for initialization=100 FILE a file with the estimate of the relative Delta F for each component of the target and of the global c(t)=DELTAFS PRINT_STRIDE stride for printing to DELTAFS file, in units of PACE=100

which, if your MD code passes the temperature to PLUMED, is equivalent to:

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
ecvThe ECV_MULTITHERMAL action with label ecv calculates the following quantities:
 Quantity   
 Type   
 Description  
ecv.ene
scalar
the value of the argument named ene: ECV_MULTITHERMALExpand a simulation to sample multiple temperatures simultaneously. This action has hidden defaults. More details ARGthe label of the internal energy of the system=ene TEMP_MAXthe maximum of the temperature range=800
ecv: ECV_MULTITHERMALExpand a simulation to sample multiple temperatures simultaneously. This action uses the defaults shown here. More details ARGthe label of the internal energy of the system=ene TEMP_MAXthe maximum of the temperature range=800  TEMP temperature=-1
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.ene PACEhow often the bias is updated=500
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.ene PACEhow often the bias is updated=500  OBSERVATION_STEPS number of unbiased initial PACE steps to collect statistics for initialization=100 FILE a file with the estimate of the relative Delta F for each component of the target and of the global c(t)=DELTAFS PRINT_STRIDE stride for printing to DELTAFS file, in units of PACE=100

If instead the pressure is fixed and the volume changes, you shuld calculate the internal energy first, $U=E+pV$

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
intEneThe CUSTOM action with label intEne calculates the following quantities:
 Quantity   
 Type   
 Description  
intEne
scalar
an arbitrary function: CUSTOMCalculate a combination of variables using a custom expression. More details PERIODICif the output of your function is periodic then you should specify the periodicity of the function=NO ARGthe values input to this function=ene,vol FUNCthe function you wish to evaluate=x+0.06022140857*y
ecvThe ECV_MULTITHERMAL action with label ecv calculates the following quantities:
 Quantity   
 Type   
 Description  
ecv.intEne
scalar
the value of the argument named intEne: ECV_MULTITHERMALExpand a simulation to sample multiple temperatures simultaneously. This action has hidden defaults. More details ARGthe label of the internal energy of the system=intEne TEMP_MAXthe maximum of the temperature range=800
ecv: ECV_MULTITHERMALExpand a simulation to sample multiple temperatures simultaneously. This action uses the defaults shown here. More details ARGthe label of the internal energy of the system=intEne TEMP_MAXthe maximum of the temperature range=800  TEMP temperature=-1
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.intEne PACEhow often the bias is updated=500
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.intEne PACEhow often the bias is updated=500  OBSERVATION_STEPS number of unbiased initial PACE steps to collect statistics for initialization=100 FILE a file with the estimate of the relative Delta F for each component of the target and of the global c(t)=DELTAFS PRINT_STRIDE stride for printing to DELTAFS file, in units of PACE=100

Notice that $p=0.06022140857$ corresponds to 1 bar when using the default PLUMED units.

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 label of the internal energy 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 label of the internal energy of the system
TEMP	compulsory	-1	temperature
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

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)