ECV_LINEAR

	This is part of the opes module
	It is only available if you configure PLUMED with ./configure –enable-modules=opes . Furthermore, this feature is still being developed so take care when using it and report any problems on the mailing list.

Linear expansion, according to a parameter lambda.

This can be used e.g. for thermodynamic integration, or for multibaric simulations, in which case lambda=pressure. It can also be used for multithermal simulations, but for simplicity it is more convenient to use ECV_MULTITHERMAL.

The difference in Hamiltonian \(\Delta U\) is expected as ARG.

\[ \Delta u_\lambda=\beta \lambda \Delta U\, . \]

Use the DIMENSIONLESS flag to avoid multiplying for the inverse temperature \(\beta\).

By defauly the needed steps in lambda are automatically guessed from few initial unbiased MD steps, as descibed in [70]. Otherwise one can set this number with LAMBDA_STEPS. In both cases the steps will be uniformly distriuted. Finally, one can use instead the keyword LAMBDA_SET_ALL and explicitly provide each lambda value.

Examples

Typical multibaric simulation:

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

vol: VOLUME The VOLUME action with label vol calculates a single scalar value
ecv: ECV_LINEAR ...
   
ARG
compulsory keyword 
the label of the Hamiltonian difference \f$\Delta U\f$ 
=vol 
   
TEMP
compulsory keyword ( default=-1 )
temperature. 
=300 
   
LAMBDA
compulsory keyword ( default=0 )
the lambda at which the underlying simulation runs 
=0.06022140857*2000 #2 kbar 
   
LAMBDA_MIN
( default=0 ) the minimum of the lambda range 
=0.06022140857 #1 bar 
   
LAMBDA_MAX
( default=1 ) the maximum of the lambda range 
=0.06022140857*4000 #4 kbar 
...The ECV_LINEAR action with label ecv calculates a single scalar value
opes: OPES_EXPANDED 
ARG
compulsory keyword 
the label of the ECVs that define the expansion. 
=ecv.vol 
PACE
compulsory keyword 
how often the bias is updated 
=500 The OPES_EXPANDED action with label opes calculates a single scalar value

Typical thermodynamic integration:

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

DeltaU: EXTRACV 
NAME
compulsory keyword 
name of the CV as computed by the MD engine 
=energy_difference The EXTRACV action with label DeltaU calculates a single scalar value
ecv: ECV_LINEAR 
ARG
compulsory keyword 
the label of the Hamiltonian difference \f$\Delta U\f$ 
=DeltaU 
TEMP
compulsory keyword ( default=-1 )
temperature. 
=300 The ECV_LINEAR action with label ecv calculates a single scalar value
opes: OPES_EXPANDED 
ARG
compulsory keyword 
the label of the ECVs that define the expansion. 
=ecv.* 
PACE
compulsory keyword 
how often the bias is updated 
=100 The OPES_EXPANDED action with label opes calculates a single scalar value

Notice that by defauly LAMBDA=0, LAMBDA_MIN=0 and LAMBDA_MAX=1, which is the typical case for thermodynamic integration.

Glossary of keywords and components

Compulsory keywords

TEMP	( default=-1 ) temperature. If not specified tries to get it from MD engine
ARG	the label of the Hamiltonian difference \(\Delta U\)
LAMBDA	( default=0 ) the lambda at which the underlying simulation runs

Options

NUMERICAL_DERIVATIVES	( default=off ) calculate the derivatives for these quantities numerically
DIMENSIONLESS	( default=off ) ARG is considered dimensionless rather than an energy, thus is not multiplied by \(\beta\)
GEOM_SPACING	( default=off ) use geometrical spacing in lambda instead of linear spacing
LAMBDA_MIN	( default=0 ) the minimum of the lambda range
LAMBDA_MAX	( default=1 ) the maximum of the lambda range
LAMBDA_STEPS	uniformly place the lambda values, for a total of LAMBDA_STEPS
LAMBDA_SET_ALL	manually set all the lamdbas