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Wed, Feb 5, 05:06
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rLAMMPS lammps
pair_soft.html
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<HTML>
<CENTER><A
HREF =
"http://lammps.sandia.gov"
>
LAMMPS WWW Site
</A>
-
<A
HREF =
"Manual.html"
>
LAMMPS Documentation
</A>
-
<A
HREF =
"Section_commands.html#comm"
>
LAMMPS Commands
</A>
</CENTER>
<HR>
<H3>
pair_style soft command
</H3>
<P><B>
Syntax:
</B>
</P>
<PRE>
pair_style soft cutoff
</PRE>
<UL><LI>
cutoff = global cutoff for soft interactions (distance units)
</UL>
<P><B>
Examples:
</B>
</P>
<PRE>
pair_style soft 2.5
pair_coeff * * 0.0 60.0
pair_coeff 1 1 0.0 60.0 3.0
</PRE>
<P><B>
Description:
</B>
</P>
<P>
Style
<I>
soft
</I>
computes pairwise interactions with the formula
</P>
<CENTER><IMG
SRC =
"Eqs/pair_soft.jpg"
>
</CENTER>
<P>
It is useful for pushing apart overlapping atoms, since it does not
blow up as r goes to 0. A is a pre-factor that varies in time from
the start to the end of the run. The
<A
HREF =
"run.html"
>
run
</A>
command documents
how to make the ramping take place across multiple runs. Rc is the
cutoff.
</P>
<P>
The following coefficients must be defined for each pair of atoms
types via the
<A
HREF =
"pair_coeff.html"
>
pair_coeff
</A>
command as in the examples
above, or in the data file or restart files read by the
<A
HREF =
"read_data.html"
>
read_data
</A>
or
<A
HREF =
"read_restart.html"
>
read_restart
</A>
commands:
</P>
<UL><LI>
Astart (energy units)
<LI>
Astop (energy units)
<LI>
cutoff (distance units)
</UL>
<P>
Astart and Astop are the values of the prefactor at the start and end
of the next run. At intermediate times the value of A will be ramped
between these 2 values. Note that before performing a 2nd run, you
will want to adjust the values of Astart and Astop for all type pairs,
or switch to a new pair style.
</P>
<P>
The last coefficient is optional. If not specified, the global soft
cutoff is used.
</P>
<P>
If the pair_coeff command is not used to define coefficients for a
particular I != J type pair, the mixing rule for Astart and Astop is
as follows:
</P>
<PRE>
A_ij = sqrt(A_i * A_j)
</PRE>
<P><B>
Restrictions:
</B>
none
</P>
<P><B>
Related commands:
</B>
</P>
<P><A
HREF =
"pair_coeff.html"
>
pair_coeff
</A>
</P>
<P><B>
Default:
</B>
none
</P>
</HTML>
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