This is part of the colvar module

Calculate the dipole moment for a group of atoms.

Description of components

By default the value of the calculated quantity can be referenced elsewhere in the input file by using the label of the action. Alternatively this Action can be used to be used to calculate the following quantities by employing the keywords listed below. These quanties 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 Keyword Description
x COMPONENTS the x-component of the dipole
y COMPONENTS the y-component of the dipole
z COMPONENTS the z-component of the dipole
The atoms involved can be specified using
GROUP the group of atoms we are calculating the dipole moment for. For more information on how to specify lists of atoms see Groups and Virtual Atoms
NUMERICAL_DERIVATIVES ( default=off ) calculate the derivatives for these quantities numerically

( default=off ) calculate the x, y and z components of the dipole separately and store them as label.x, label.y and label.z

The following tells plumed to calculate the dipole of the group of atoms containing the atoms from 1-10 and print it every 5 steps
(see also PRINT)
If the total charge Q of the group in non zero, then a charge Q/N will be subtracted to every atom, where N is the number of atoms. This implies that the dipole (which for a charged system depends on the position) is computed on the geometric center of the group.