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 \(\beta\).

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 
   
MIN_LAMBDA
( default=0 ) the minimum of the lambda range 
=0.06022140857 #1 bar 
   
MAX_LAMBDA
( 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, MIN_LAMBDA=0 and MAX_LAMBDA=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 \(\beta\)
MIN_LAMBDA	( default=0 ) the minimum of the lambda range
MAX_LAMBDA	( default=1 ) the maximum of the lambda range
STEPS_LAMBDA	uniformly place the lambda values, for a total of STEPS_LAMBDA
SET_ALL_LAMBDAS	manually set all the lamdbas