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pair_style_dpd.html
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rLAMMPS lammps
pair_style_dpd.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 dpd command
</H3>
<P><B>
Syntax:
</B>
</P>
<PRE>
pair_style dpd T cutoff seed
</PRE>
<UL><LI>
T = temperature (temperature units)
<LI>
cutoff = global cutoff for DPD interactions (distance units)
<LI>
seed = random # seed (integer > 0 and
< 900000000
)
</
UL
>
<P><B>
Examples:
</B>
</P>
<PRE>
pair_style dpd 1.0 2.5 34387
pair_coeff * * 3.0 1.0
pair_coeff 1 1 3.0 1.0 1.0
</PRE>
<P><B>
Description:
</B>
</P>
<P>
Style
<I>
dpd
</I>
computes a force field for dissipative particle dynamics
(DPD) following the exposition in
<A
HREF =
"#Groot"
>
(Groot)
</A>
. The force
on atom I due to atom J is given as a sum of 3 terms
</P>
<CENTER><IMG
SRC =
"Eqs/pair_dpd.jpg"
>
</CENTER>
<P>
where FC is a conservative force, FD is a dissipative force, and FR is
a random force. Rij is a unit vector in the direction Ri - Rj, Vij is
the vector difference in velocities of the two atoms = Vi - Vj, alpha
is a Gaussian random number with zero mean and unit variance, dt is
the timestep size, and w(r) is a weighting factor that varies between
0 and 1. Rc is the cutoff. Sigma is set equal to sqrt(2 T gamma),
where T is a parameter in the pair_style command.
</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>
A (force units)
<LI>
gamma (force/velocity units)
<LI>
cutoff (distance units)
</UL>
<P>
The last coefficient is optional. If not specified, the global DPD
cutoff is used. Note that sigma is set equal to sqrt(2 T gamma),
where T is the temperature set by the
<A
HREF =
"pair_style.html"
>
pair_style
</A>
command so it does not need to be specified.
</P>
<P><B>
Restrictions:
</B>
none
</P>
<P>
This style is part of the "dpd" package. It is only enabled if LAMMPS
was built with those package. See the
<A
HREF =
"Section_start.html#2_2"
>
Making
LAMMPS
</A>
section for more info.
</P>
<P>
The
<I>
dpd
</I>
potential does not support the
<A
HREF =
"pair_modify.hmtl"
>
pair_modify
</A>
<I>
mix
</I>
option. Coefficients for all i,j
pairs must be specified explicitly.
</P>
<P><B>
Related commands:
</B>
</P>
<P><A
HREF =
"pair_coeff.html"
>
pair_coeff
</A>
</P>
<P><B>
Default:
</B>
none
</P>
<HR>
<A
NAME =
"Groot"
></A>
<P><B>
(Groot)
</B>
Groot and Warren, J Chem Phys, 107, 4423-35 (1997).
</P>
</HTML>
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