"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)

:line

mass command :h3

[Syntax:]

mass I value :pre

I = atom type (see asterik form below)
value = mass :ul

[Examples:]

mass 1 1.0
mass * 62.5
mass 2* 62.5 :pre

[Description:]

Set the mass for all atoms of one or more atom types.  Mass values can
also be set in the "read_data"_read_data.html data file.  See the
"units"_units.html command for what mass units to use.

Most atom styles require masses to be specified.  One exception is
"atom_style granular"_atom_style.html, where masses are defined for
individual atoms, not types.  "Pair_style eam"_pair_eam.html defines
the masses of atom types in the EAM potential file.

I can be specified in one of two ways.  An explicit numeric value can
be used, as in the 1st example above.  Or a wild-card asterik can be
used to set the mass for multiple atom types.  This takes the form "*"
or "*n" or "n*" or "m*n".  If N = the number of atom types, then an
asterik with no numeric values means all types from 1 to N.  A leading
asterik means all types from 1 to n (inclusive).  A trailing asterik
means all types from n to N (inclusive).  A middle asterik means all
types from m to n (inclusive).

A line in a data file that specifies mass uses the same format as the
arguments of the mass command in an input script, except that no
wild-card asterik can be used.  For example, under the "Masses"
section of a data file, the line that corresponds to the 1st example
above would be listed as

1 1.0 :pre

[Restrictions:]

This command must come after the simulation box is defined by a
"read_data"_read_data.html, "read_restart"_read_restart.html, or
"create_box"_create_box.html command.

All masses must be defined before a simulation is run (if the atom
style requires masses be set).  They must also all be defined before a
"velocity"_velocity.html or "fix shake"_fix_shake.html command is
used.

[Related commands:] none

[Default:] none