2006-09-22 00:22:34 +08:00
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"LAMMPS WWW Site"_lws - "LAMPS 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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units command :h3
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[Syntax:]
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units style :pre
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style = {lj} or {real} or {metal} :ul
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[Examples:]
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units metal
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units lj :pre
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[Description:]
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This command sets the style of units used for a simulation. It
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detemines the units of all quantities specified in the input script
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and data file, as well as quantities output to the screen, log file,
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and dump files. Typically, this command is used at the very beginning
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of an input script.
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2007-01-31 06:10:35 +08:00
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For real and metallic units, LAMMPS uses physical constants from
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2007-01-31 01:20:42 +08:00
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www.physics.nist.gov. For the definition of Kcal in real units, LAMMPS
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uses the thermochemical calorie = 4.184 J.
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2006-09-22 00:22:34 +08:00
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For style {lj}, all quantities are unitless:
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distance = sigma
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time = tau
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mass = one
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energy = epsilon
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velocity = sigma/tau
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force = epsilon/sigma
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temperature = reduced LJ temperature
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pressure = reduced LJ pressure
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charge = reduced LJ charge
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electric field = force/charge :ul
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For style {real}, these are the units:
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distance = Angstroms
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time = femtoseconds
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mass = grams/mole
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energy = Kcal/mole
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velocity = Angstroms/femtosecond
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force = Kcal/mole-Angstrom
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temperature = degrees K
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pressure = atmospheres
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charge = multiple of electron charge (+1.0 is a proton)
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electric field = volts/Angstrom :ul
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For style {metal}, these are the units:
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distance = Angstroms
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time = picoseconds
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mass = grams/mole
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energy = eV
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velocity = Angstroms/picosecond
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force = eV/Angstrom
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temperature = degrees K
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pressure = bars
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charge = multiple of electron charge (+1.0 is a proton)
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electric field = volts/Angstrom :ul
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This command also sets the timestep size and neighbor skin distance to
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default values for each style. For style {lj} these are dt = 0.005
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tau and skin = 0.3 sigma. For style {real} these are dt = 1.0 fmsec
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and skin = 2.0 Angstroms. For style {metal} these are dt = 0.001 psec
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and skin = 2.0 Angstroms.
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[Restrictions:]
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This command cannot be used after the simulation box is defined by a
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"read_data"_read_data.html or "create_box"_create_box.html command.
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[Related commands:] none
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[Default:]
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units lj :pre
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