EXTRACV

This is part of the colvar module

Allow PLUMED to use collective variables computed in the MD engine.

This feature requires the MD engine to use special instructions to pass to PLUMED the value of some pre-computed collective variable. Check the documentation of the MD code to find out which collective variables can be computed and passed to PLUMED. These variables can then be accessed by name using the EXTRACV action.

Examples

This example takes the lambda variable pre-computed in GROMACS and apply to it a restraint to keep it close to the value 3.

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

contract shortcuts

l: EXTRACV 
NAME
compulsory keyword 
name of the CV as computed by the MD engine 
=lambda The EXTRACV action with label l calculates a single scalar value
RESTRAINT 
ARG
the values the harmonic restraint acts upon. 
=l 
KAPPA
compulsory keyword ( default=0.0 )
specifies that the restraint is harmonic and what the values of the force constants
on each of the variables are 
=10 
AT
compulsory keyword 
the position of the restraint 
=3 The RESTRAINT action with label 

lambda: PUT 
UNIT
compulsory keyword 
the unit of the quantity that is being passed to PLUMED through this value. 
=number 
SHAPE
compulsory keyword ( default=0 )
the shape of the value that is being passed to PLUMED 
=0 
MUTABLE
( default=off ) can plumed change the value of the pointer that is passed from the
MD code 
 
PERIODIC
compulsory keyword 
if the value being passed to plumed is periodic then you should specify the periodicity
of the function. 
=NO The PUT action with label lambda calculates a single scalar value
l: COMBINE 
ARG
compulsory keyword 
the values input to this function 
=lambda 
PERIODIC
compulsory keyword 
if the output of your function is periodic then you should specify the periodicity
of the function. 
=NO The COMBINE action with label l calculates a single scalar value

Glossary of keywords and components

Description of components

Quantity	Description
.#!value	the value of the CV that was passed from the MD code to PLUMED

Compulsory keywords

NAME	name of the CV as computed by the MD engine