Adds harmonic and/or linear restraints on one or more variables.

Either or both of SLOPE and KAPPA must be present to specify the linear and harmonic force constants respectively. The resulting potential is given by:

The number of components for any vector of force constants must be equal to the number of arguments to the action.

Additional material and examples can be also found in the tutorial lugano-2

Examples

The following input tells plumed to restrain the distance between atoms 3 and 5 and the distance between atoms 2 and 4, at different equilibrium values, and to print the energy of the restraint

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

the pair of atom that we are calculating the distance between.

=3,5 The DISTANCE action with label d1 calculates a single scalar valued2: DISTANCE

ATOMS

the pair of atom that we are calculating the distance between.

=2,4 The DISTANCE action with label d2 calculates a single scalar valuePRINT

ARG

the input for this action is the scalar output from one or more other actions.

=restraint.bias The PRINT action with label

Glossary of keywords and components

Description of components

By default this Action calculates the following quantities. These quantities can be referenced elsewhere in the input by using this Action's label followed by a dot and the name of the quantity required from the list below.

Quantity

Description

bias

the instantaneous value of the bias potential

force2

the instantaneous value of the squared force due to this bias potential

Compulsory keywords

SLOPE

( default=0.0 ) specifies that the restraint is linear and what the values of the force constants on each of the variables are

KAPPA

( default=0.0 ) specifies that the restraint is harmonic and what the values of the force constants on each of the variables are

AT

the position of the restraint

Options

ARG

the arguments on which the bias is acting. You can use multiple instances of this keyword i.e. ARG1, ARG2, ARG3...