"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

units command :h3

[Syntax:]

units style :pre

style = {lj} or {real} or {metal} :ul

[Examples:]

units metal
units lj :pre

[Description:]

This command sets the style of units used for a simulation.  It
detemines the units of all quantities specified in the input script
and data file, as well as quantities output to the screen, log file,
and dump files.  Typically, this command is used at the very beginning
of an input script.

For real and metallic units, LAMMPS uses physical constants from
www.physics.nist.gov. For the definition of Kcal in real units, LAMMPS
uses the thermochemical calorie = 4.184 J.

For style {lj}, all quantities are unitless:

distance = sigma
time = tau
mass = one
energy = epsilon
velocity = sigma/tau
force = epsilon/sigma
temperature = reduced LJ temperature
pressure = reduced LJ pressure
charge = reduced LJ charge
dipole = reduced LJ dipole moment
electric field = force/charge :ul

For style {real}, these are the units:

distance = Angstroms
time = femtoseconds
mass = grams/mole
energy = Kcal/mole 
velocity = Angstroms/femtosecond 
force = Kcal/mole-Angstrom
temperature = degrees K
pressure = atmospheres
charge = multiple of electron charge (+1.0 is a proton)
dipole = charge*Angstroms
electric field = volts/Angstrom :ul

For style {metal}, these are the units:

distance = Angstroms
time = picoseconds
mass = grams/mole
energy = eV
velocity = Angstroms/picosecond 
force = eV/Angstrom
temperature = degrees K
pressure = bars
charge = multiple of electron charge (+1.0 is a proton)
dipole = charge*Angstroms
electric field = volts/Angstrom :ul

This command also sets the timestep size and neighbor skin distance to
default values for each style.  For style {lj} these are dt = 0.005
tau and skin = 0.3 sigma.  For style {real} these are dt = 1.0 fmsec
and skin = 2.0 Angstroms.  For style {metal} these are dt = 0.001 psec
and skin = 2.0 Angstroms.

[Restrictions:]

This command cannot be used after the simulation box is defined by a
"read_data"_read_data.html or "create_box"_create_box.html command.

[Related commands:] none

[Default:]

units lj :pre