MASS_SCALAR
This is part of the colvar module

Get the mass of one or multiple atoms

Examples
Glossary of keywords and components
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 calculate the following quantities by employing the keywords listed below. 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
.#!value the MASS of the atom
The atoms involved can be specified using
ATOM the atom number. For more information on how to specify lists of atoms see Groups and Virtual Atoms
ATOMS the atom numbers that you would like to store the masses and charges of. For more information on how to specify lists of atoms see Groups and Virtual Atoms
Options
NUMERICAL_DERIVATIVES ( default=off ) calculate the derivatives for these quantities numerically
NOPBC

( default=off ) ignore the periodic boundary conditions when calculating distances