forked from lijiext/lammps
84 lines
2.8 KiB
Plaintext
84 lines
2.8 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Section_commands.html#comm)
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:line
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mass command :h3
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[Syntax:]
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mass I value :pre
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I = atom type (see asterisk form below)
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value = mass :ul
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[Examples:]
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mass 1 1.0
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mass * 62.5
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mass 2* 62.5 :pre
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[Description:]
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Set the mass for all atoms of one or more atom types. Per-type mass
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values can also be set in the "read_data"_read_data.html data file
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using the "Masses" keyword. See the "units"_units.html command for
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what mass units to use.
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The I index can be specified in one of two ways. An explicit numeric
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value can be used, as in the 1st example above. Or a wild-card
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asterisk can be used to set the mass for multiple atom types. This
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takes the form "*" or "*n" or "n*" or "m*n". If N = the number of
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atom types, then an asterisk with no numeric values means all types
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from 1 to N. A leading asterisk means all types from 1 to n
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(inclusive). A trailing asterisk means all types from n to N
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(inclusive). A middle asterisk means all types from m to n
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(inclusive).
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A line in a "data file"_read_data.html that follows the "Masses"
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keyword specifies mass using the same format as the arguments of the
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mass command in an input script, except that no wild-card asterisk can
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be used. For example, under the "Masses" section of a data file, the
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line that corresponds to the 1st example above would be listed as
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1 1.0 :pre
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Note that the mass command can only be used if the "atom
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style"_atom_style.html requires per-type atom mass to be set.
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Currently, all but the {granular} and {peri} styles do. They require
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mass to be set for individual particles, not types. Per-atom masses
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are defined in the data file read by the "read_data"_read_data.html
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command, or set to default values by the
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"create_atoms"_create_atoms.html command. Per-atom masses can also be
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set to new values by the "set diameter"_set.html or "set
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density"_set.html command.
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Also note that "pair_style eam"_pair_eam.html defines the masses of
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atom types in the EAM potential file, in which case the mass command
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is normally not used.
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If you define a "hybrid atom style"_atom_style.html which includes one
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(or more) sub-styles which require per-type mass and one (or more)
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sub-styles which require per-atom mass, then you must define both.
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However, in this case the per-type mass will be ignored; only the
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per-atom mass will be used by LAMMPS.
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[Restrictions:]
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This command must come after the simulation box is defined by a
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"read_data"_read_data.html, "read_restart"_read_restart.html, or
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"create_box"_create_box.html command.
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All masses must be defined before a simulation is run. They must also
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all be defined before a "velocity"_velocity.html or "fix
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shake"_fix_shake.html command is used.
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The mass assigned to any type or atom must be > 0.0.
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[Related commands:] none
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[Default:] none
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