forked from lijiext/lammps
180 lines
7.3 KiB
HTML
180 lines
7.3 KiB
HTML
|
<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 buck/disp/coul/long command
|
||
|
|
</H3>
|
||
|
|
<H3>pair_style buck/disp/coul/long/omp command
|
||
|
|
</H3>
|
||
|
|
<P><B>Syntax:</B>
|
||
|
|
</P>
|
||
|
|
<PRE>pair_style buck/disp/coul/long flag_buck flag_coul cutoff (cutoff2)
|
||
|
|
</PRE>
|
||
|
|
<UL><LI>flag_buck = <I>long</I> or <I>cut</I>
|
||
|
|
|
||
|
|
<PRE> <I>long</I> = use Kspace long-range summation for the dispersion term 1/r^6
|
||
|
|
<I>cut</I> = use a cutoff
|
||
|
|
</PRE>
|
||
|
|
<LI>flag_coul = <I>long</I> or <I>off</I>
|
||
|
|
|
||
|
|
<PRE> <I>long</I> = use Kspace long-range summation for the Coulombic term 1/r
|
||
|
|
<I>off</I> = omit the Coulombic term
|
||
|
|
</PRE>
|
||
|
|
<LI>cutoff = global cutoff for Buckingham (and Coulombic if only 1 cutoff) (distance units)
|
||
|
|
|
||
|
|
<LI>cutoff2 = global cutoff for Coulombic (optional) (distance units)
|
||
|
|
</UL>
|
||
|
|
<P><B>Examples:</B>
|
||
|
|
</P>
|
||
|
|
<PRE>pair_style buck/disp/coul/long cut off 2.5
|
||
|
|
pair_style buck/disp/coul/long cut long 2.5 4.0
|
||
|
|
pair_style buck/disp/coul/long long long 2.5 4.0
|
||
|
|
pair_coeff * * 1 1
|
||
|
|
pair_coeff 1 1 1 3 4
|
||
|
|
</PRE>
|
||
|
|
<P><B>Description:</B>
|
||
|
|
</P>
|
||
|
|
<P>The <I>buck/disp/coul/long</I> style computes a Buckingham potential (exp/6
|
||
|
|
instead of Lennard-Jones 12/6) and Coulombic potential, given by
|
||
|
|
</P>
|
||
|
|
<CENTER><IMG SRC = "Eqs/pair_buck.jpg">
|
||
|
|
</CENTER>
|
||
|
|
<CENTER><IMG SRC = "Eqs/pair_coulomb.jpg">
|
||
|
|
</CENTER>
|
||
|
|
<P>Rc is the cutoff. If one cutoff is specified in the pair_style
|
||
|
|
command, it is used for both the Buckingham and Coulombic terms. If
|
||
|
|
two cutoffs are specified, they are used as cutoffs for the Buckingham
|
||
|
|
and Coulombic terms respectively.
|
||
|
|
</P>
|
||
|
|
<P>The purpose of this pair style is to capture long-range interactions
|
||
|
|
resulting from both attractive 1/r^6 Buckingham and Coulombic 1/r
|
||
|
|
interactions. This is done by use of the <I>flag_buck</I> and <I>flag_coul</I>
|
||
|
|
settings. The "<A HREF = "#Ismail">Ismail</A> paper has more details on when it is
|
||
|
|
appropriate to include long-range 1/r^6 interactions, using this
|
||
|
|
potential.
|
||
|
|
</P>
|
||
|
|
<P>If <I>flag_buck</I> is set to <I>long</I>, no cutoff is used on the Buckingham
|
||
|
|
1/r^6 dispersion term. The long-range portion is calculated by using
|
||
|
|
the <A HREF = "kspace_style.html">kspace_style ewald/n</A> command. The specified
|
||
|
|
Buckingham cutoff then determines which portion of the Buckingham
|
||
|
|
interactions are computed directly by the pair potential versus which
|
||
|
|
part is computed in reciprocal space via the Kspace style. If
|
||
|
|
<I>flag_buck</I> is set to <I>cut</I>, the Buckingham interactions are simply
|
||
|
|
cutoff, as with <A HREF = "pair_buck.html">pair_style buck</A>.
|
||
|
|
</P>
|
||
|
|
<P>If <I>flag_coul</I> is set to <I>long</I>, no cutoff is used on the Coulombic
|
||
|
|
interactions. The long-range portion is calculated by using any
|
||
|
|
style, including <I>ewald/n</I> of the <A HREF = "kspace_style.html">kspace_style</A>
|
||
|
|
command. Note that if <I>flag_buck</I> is also set to long, then only the
|
||
|
|
<I>ewald/n</I> Kspace style can perform the long-range calculations for
|
||
|
|
both the Buckingham and Coulombic interactions. If <I>flag_coul</I> is set
|
||
|
|
to <I>off</I>, Coulombic interactions are not computed.
|
||
|
|
</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 (energy units)
|
||
|
|
<LI>rho (distance units)
|
||
|
|
<LI>C (energy-distance^6 units)
|
||
|
|
<LI>cutoff (distance units)
|
||
|
|
<LI>cutoff2 (distance units)
|
||
|
|
</UL>
|
||
|
|
<P>The second coefficient, rho, must be greater than zero.
|
||
|
|
</P>
|
||
|
|
<P>The latter 2 coefficients are optional. If not specified, the global
|
||
|
|
Buckingham and Coulombic cutoffs specified in the pair_style command
|
||
|
|
are used. If only one cutoff is specified, it is used as the cutoff
|
||
|
|
for both Buckingham and Coulombic interactions for this type pair. If
|
||
|
|
both coefficients are specified, they are used as the Buckingham and
|
||
|
|
Coulombic cutoffs for this type pair. Note that if you are using
|
||
|
|
<I>flag_buck</I> set to <I>long</I>, you cannot specify a Buckingham cutoff for
|
||
|
|
an atom type pair, since only one global Buckingham cutoff is allowed.
|
||
|
|
Similarly, if you are using <I>flag_coul</I> set to <I>long</I>, you cannot
|
||
|
|
specify a Coulombic cutoff for an atom type pair, since only one
|
||
|
|
global Coulombic cutoff is allowed.
|
||
|
|
</P>
|
||
|
|
<HR>
|
||
|
|
|
||
|
|
<P>Styles with a <I>cuda</I>, <I>gpu</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-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>This pair styles does not support mixing. Thus, coefficients for all
|
||
|
|
I,J pairs must be specified explicitly.
|
||
|
|
</P>
|
||
|
|
<P>This pair style supports the <A HREF = "pair_modify.html">pair_modify</A> shift
|
||
|
|
option for the energy of the exp() and 1/r^6 portion of the pair
|
||
|
|
interaction, assuming <I>flag_buck</I> is <I>cut</I>.
|
||
|
|
</P>
|
||
|
|
<P>This pair style does not support the <A HREF = "pair_modify.html">pair_modify</A>
|
||
|
|
shift option for the energy of the Buckingham portion of the pair
|
||
|
|
interaction.
|
||
|
|
</P>
|
||
|
|
<P>This 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>This pair style write its 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>This pair style supports the use of the <I>inner</I>, <I>middle</I>, and <I>outer</I>
|
||
|
|
keywords of the <A HREF = "run_style.html">run_style respa</A> command, meaning the
|
||
|
|
pairwise forces can be partitioned by distance at different levels of
|
||
|
|
the rRESPA hierarchy. See the <A HREF = "run_style.html">run_style</A> command for
|
||
|
|
details.
|
||
|
|
</P>
|
||
|
|
<HR>
|
||
|
|
|
||
|
|
<P><B>Restrictions:</B>
|
||
|
|
</P>
|
||
|
|
<P>This style is part of the KSPACE package. It is 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. Note that
|
||
|
|
the KSPACE package is installed by default.
|
||
|
|
</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 = "Ismail"></A>
|
||
|
|
|
||
|
|
<P><B>(Ismail)</B> Ismail, Tsige, In 't Veld, Grest, Molecular Physics
|
||
|
|
(accepted) (2007).
|
||
|
|
</P>
|
||
|
|
</HTML>
|