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rLAMMPS lammps
pair_class2.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 lj/class2 command
</H3>
<H3>
pair_style lj/class2/cuda command
</H3>
<H3>
pair_style lj/class2/gpu command
</H3>
<H3>
pair_style lj/class2/kk command
</H3>
<H3>
pair_style lj/class2/omp command
</H3>
<H3>
pair_style lj/class2/coul/cut command
</H3>
<H3>
pair_style lj/class2/coul/cut/cuda command
</H3>
<H3>
pair_style lj/class2/coul/cut/kk command
</H3>
<H3>
pair_style lj/class2/coul/cut/omp command
</H3>
<H3>
pair_style lj/class2/coul/long command
</H3>
<H3>
pair_style lj/class2/coul/long/cuda command
</H3>
<H3>
pair_style lj/class2/coul/long/gpu command
</H3>
<H3>
pair_style lj/class2/coul/long/kk command
</H3>
<H3>
pair_style lj/class2/coul/long/omp command
</H3>
<P><B>
Syntax:
</B>
</P>
<PRE>
pair_style style args
</PRE>
<UL><LI>
style =
<I>
lj/class2
</I>
or
<I>
lj/class2/coul/cut
</I>
or
<I>
lj/class2/coul/long
</I>
<LI>
args = list of arguments for a particular style
</UL>
<PRE>
<I>
lj/class2
</I>
args = cutoff
cutoff = global cutoff for class 2 interactions (distance units)
<I>
lj/class2/coul/cut
</I>
args = cutoff (cutoff2)
cutoff = global cutoff for class 2 (and Coulombic if only 1 arg) (distance units)
cutoff2 = global cutoff for Coulombic (optional) (distance units)
<I>
lj/class2/coul/long
</I>
args = cutoff (cutoff2)
cutoff = global cutoff for class 2 (and Coulombic if only 1 arg) (distance units)
cutoff2 = global cutoff for Coulombic (optional) (distance units)
</PRE>
<P><B>
Examples:
</B>
</P>
<PRE>
pair_style lj/class2 10.0
pair_coeff * * 100.0 2.5
pair_coeff 1 2* 100.0 2.5 9.0
</PRE>
<PRE>
pair_style lj/class2/coul/cut 10.0
pair_style lj/class2/coul/cut 10.0 8.0
pair_coeff * * 100.0 3.0
pair_coeff 1 1 100.0 3.5 9.0
pair_coeff 1 1 100.0 3.5 9.0 9.0
</PRE>
<PRE>
pair_style lj/class2/coul/long 10.0
pair_style lj/class2/coul/long 10.0 8.0
pair_coeff * * 100.0 3.0
pair_coeff 1 1 100.0 3.5 9.0
</PRE>
<P><B>
Description:
</B>
</P>
<P>
The
<I>
lj/class2
</I>
styles compute a 6/9 Lennard-Jones potential given by
</P>
<CENTER><IMG
SRC =
"Eqs/pair_class2.jpg"
>
</CENTER>
<P>
Rc is the cutoff.
</P>
<P>
The
<I>
lj/class2/coul/cut
</I>
and
<I>
lj/class2/coul/long
</I>
styles add a
Coulombic term as described for the
<A
HREF =
"pair_lj.html"
>
lj/cut
</A>
pair styles.
</P>
<P>
See
<A
HREF =
"#Sun"
>
(Sun)
</A>
for a description of the COMPASS class2 force field.
</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, or by mixing as described below:
</P>
<UL><LI>
epsilon (energy units)
<LI>
sigma (distance units)
<LI>
cutoff1 (distance units)
<LI>
cutoff2 (distance units)
</UL>
<P>
The latter 2 coefficients are optional. If not specified, the global
class 2 and Coulombic cutoffs are used. If only one cutoff is
specified, it is used as the cutoff for both class 2 and Coulombic
interactions for this type pair. If both coefficients are specified,
they are used as the class 2 and Coulombic cutoffs for this type pair.
You cannot specify 2 cutoffs for style
<I>
lj/class2
</I>
, since it has no
Coulombic terms.
</P>
<P>
For
<I>
lj/class2/coul/long
</I>
only the class 2 cutoff can be specified
since a Coulombic cutoff cannot be specified for an individual I,J
type pair. All type pairs use the same global Coulombic cutoff
specified in the pair_style command.
</P>
<HR>
<P>
If the pair_coeff command is not used to define coefficients for a
particular I != J type pair, the mixing rule for epsilon and sigma for
all class2 potentials is to use the
<I>
sixthpower
</I>
formulas documented
by the
<A
HREF =
"pair_modify.html"
>
pair_modify
</A>
command. The
<A
HREF =
"pair_modify.html"
>
pair_modify
mix
</A>
setting is thus ignored for class2 potentials
for epsilon and sigma. However it is still followed for mixing the
cutoff distance.
</P>
<HR>
<P>
Styles with a
<I>
cuda
</I>
,
<I>
gpu
</I>
,
<I>
intel
</I>
,
<I>
kk
</I>
,
<I>
omp
</I>
, or
<I>
opt
</I>
suffix are
functionally the same as the corresponding style without the suffix.
They have been optimized to run faster, depending on your available
hardware, as discussed in
<A
HREF =
"Section_accelerate.html"
>
Section_accelerate
</A>
of the manual. The accelerated styles take the same arguments and
should produce the same results, except for round-off and precision
issues.
</P>
<P>
These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
KOKKOS, USER-OMP and OPT packages, respectively. They are only
enabled if LAMMPS was built with those packages. See the
<A
HREF =
"Section_start.html#start_3"
>
Making
LAMMPS
</A>
section for more info.
</P>
<P>
You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the
<A
HREF =
"Section_start.html#start_7"
>
-suffix command-line
switch
</A>
when you invoke LAMMPS, or you can
use the
<A
HREF =
"suffix.html"
>
suffix
</A>
command in your input script.
</P>
<P>
See
<A
HREF =
"Section_accelerate.html"
>
Section_accelerate
</A>
of the manual for
more instructions on how to use the accelerated styles effectively.
</P>
<HR>
<P><B>
Mixing, shift, table, tail correction, restart, rRESPA info
</B>
:
</P>
<P>
For atom type pairs I,J and I != J, the epsilon and sigma coefficients
and cutoff distance for all of the lj/class2 pair styles can be mixed.
Epsilon and sigma are always mixed with the value
<I>
sixthpower
</I>
. The
cutoff distance is mixed by whatever option is set by the pair_modify
command (default = geometric). See the "pair_modify" command for
details.
</P>
<P>
All of the lj/class2 pair styles support the
<A
HREF =
"pair_modify.html"
>
pair_modify
</A>
shift option for the energy of the
Lennard-Jones portion of the pair interaction.
</P>
<P>
The
<I>
lj/class2/coul/long
</I>
pair style does not support the
<A
HREF =
"pair_modify.html"
>
pair_modify
</A>
table option since a tabulation
capability has not yet been added to this potential.
</P>
<P>
All of the lj/class2 pair styles support the
<A
HREF =
"pair_modify.html"
>
pair_modify
</A>
tail option for adding a long-range
tail correction to the energy and pressure of the Lennard-Jones
portion of the pair interaction.
</P>
<P>
All of the lj/class2 pair styles write their information to
<A
HREF =
"restart.html"
>
binary
restart files
</A>
, so pair_style and pair_coeff commands do
not need to be specified in an input script that reads a restart file.
</P>
<P>
All of the lj/class2 pair styles can only be used via the
<I>
pair
</I>
keyword of the
<A
HREF =
"run_style.html"
>
run_style respa
</A>
command. They do not
support the
<I>
inner
</I>
,
<I>
middle
</I>
,
<I>
outer
</I>
keywords.
</P>
<P><B>
Restrictions:
</B>
</P>
<P>
These styles are part of the CLASS2 package. They are only enabled if
LAMMPS was built with that package. See the
<A
HREF =
"Section_start.html#start_3"
>
Making
LAMMPS
</A>
section for more info.
</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 =
"Sun"
></A>
<P><B>
(Sun)
</B>
Sun, J Phys Chem B 102, 7338-7364 (1998).
</P>
</HTML>
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