2006-09-22 00:22:34 +08:00
|
|
|
<HTML>
|
|
|
|
|
<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
|
|
|
|
|
</CENTER>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<HR>
|
|
|
|
|
|
|
|
|
|
<H3>units command
|
|
|
|
|
</H3>
|
|
|
|
|
<P><B>Syntax:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<PRE>units style
|
|
|
|
|
</PRE>
|
|
|
|
|
<UL><LI>style = <I>lj</I> or <I>real</I> or <I>metal</I>
|
|
|
|
|
</UL>
|
|
|
|
|
<P><B>Examples:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<PRE>units metal
|
|
|
|
|
units lj
|
|
|
|
|
</PRE>
|
|
|
|
|
<P><B>Description:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<P>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.
|
|
|
|
|
</P>
|
2007-01-31 06:10:35 +08:00
|
|
|
<P>For real and metallic units, LAMMPS uses physical constants from
|
2007-01-31 01:20:42 +08:00
|
|
|
www.physics.nist.gov. For the definition of Kcal in real units, LAMMPS
|
|
|
|
|
uses the thermochemical calorie = 4.184 J.
|
|
|
|
|
</P>
|
2006-09-22 00:22:34 +08:00
|
|
|
<P>For style <I>lj</I>, all quantities are unitless:
|
|
|
|
|
</P>
|
|
|
|
|
<UL><LI>distance = sigma
|
|
|
|
|
<LI>time = tau
|
|
|
|
|
<LI>mass = one
|
|
|
|
|
<LI>energy = epsilon
|
|
|
|
|
<LI>velocity = sigma/tau
|
|
|
|
|
<LI>force = epsilon/sigma
|
|
|
|
|
<LI>temperature = reduced LJ temperature
|
|
|
|
|
<LI>pressure = reduced LJ pressure
|
|
|
|
|
<LI>charge = reduced LJ charge
|
|
|
|
|
<LI>electric field = force/charge
|
|
|
|
|
</UL>
|
|
|
|
|
<P>For style <I>real</I>, these are the units:
|
|
|
|
|
</P>
|
|
|
|
|
<UL><LI>distance = Angstroms
|
|
|
|
|
<LI>time = femtoseconds
|
|
|
|
|
<LI>mass = grams/mole
|
|
|
|
|
<LI>energy = Kcal/mole
|
|
|
|
|
<LI>velocity = Angstroms/femtosecond
|
|
|
|
|
<LI>force = Kcal/mole-Angstrom
|
|
|
|
|
<LI>temperature = degrees K
|
|
|
|
|
<LI>pressure = atmospheres
|
|
|
|
|
<LI>charge = multiple of electron charge (+1.0 is a proton)
|
|
|
|
|
<LI>electric field = volts/Angstrom
|
|
|
|
|
</UL>
|
|
|
|
|
<P>For style <I>metal</I>, these are the units:
|
|
|
|
|
</P>
|
|
|
|
|
<UL><LI>distance = Angstroms
|
|
|
|
|
<LI>time = picoseconds
|
|
|
|
|
<LI>mass = grams/mole
|
|
|
|
|
<LI>energy = eV
|
|
|
|
|
<LI>velocity = Angstroms/picosecond
|
|
|
|
|
<LI>force = eV/Angstrom
|
|
|
|
|
<LI>temperature = degrees K
|
|
|
|
|
<LI>pressure = bars
|
|
|
|
|
<LI>charge = multiple of electron charge (+1.0 is a proton)
|
|
|
|
|
<LI>electric field = volts/Angstrom
|
|
|
|
|
</UL>
|
|
|
|
|
<P>This command also sets the timestep size and neighbor skin distance to
|
|
|
|
|
default values for each style. For style <I>lj</I> these are dt = 0.005
|
|
|
|
|
tau and skin = 0.3 sigma. For style <I>real</I> these are dt = 1.0 fmsec
|
|
|
|
|
and skin = 2.0 Angstroms. For style <I>metal</I> these are dt = 0.001 psec
|
|
|
|
|
and skin = 2.0 Angstroms.
|
|
|
|
|
</P>
|
|
|
|
|
<P><B>Restrictions:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<P>This command cannot be used after the simulation box is defined by a
|
|
|
|
|
<A HREF = "read_data.html">read_data</A> or <A HREF = "create_box.html">create_box</A> command.
|
|
|
|
|
</P>
|
|
|
|
|
<P><B>Related commands:</B> none
|
|
|
|
|
</P>
|
|
|
|
|
<P><B>Default:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<PRE>units lj
|
|
|
|
|
</PRE>
|
|
|
|
|
</HTML>
|
