Page Menu
Home
c4science
Search
Configure Global Search
Log In
Files
F106784438
pair_coul.html
No One
Temporary
Actions
Download File
Edit File
Delete File
View Transforms
Subscribe
Mute Notifications
Award Token
Subscribers
None
File Metadata
Details
File Info
Storage
Attached
Created
Mon, Mar 31, 14:21
Size
7 KB
Mime Type
text/html
Expires
Wed, Apr 2, 14:21 (2 d)
Engine
blob
Format
Raw Data
Handle
25273978
Attached To
rLAMMPS lammps
pair_coul.html
View Options
<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 coul/cut command
</H3>
<H3>pair_style coul/cut/omp command
</H3>
<H3>pair_style coul/debye command
</H3>
<H3>pair_style coul/debye/omp command
</H3>
<H3>pair_style coul/long command
</H3>
<H3>pair_style coul/long/omp command
</H3>
<H3>pair_style coul/long/gpu command
</H3>
<H3>pair_style coul/wolf command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>pair_style coul/cut cutoff
pair_style coul/debye kappa cutoff
pair_style coul/long cutoff
pair_style coul/long/gpu cutoff
pair_sytle coul/wolf alpha cutoff
</PRE>
<UL><LI>cutoff = global cutoff for Coulombic interactions
<LI>kappa = Debye length (inverse distance units)
<LI>alpha = damping parameter (inverse distance units)
</UL>
<P><B>Examples:</B>
</P>
<PRE>pair_style coul/cut 2.5
pair_coeff * *
pair_coeff 2 2 3.5
</PRE>
<PRE>pair_style coul/debye 1.4 3.0
pair_coeff * *
pair_coeff 2 2 3.5
</PRE>
<PRE>pair_style coul/long 10.0
pair_coeff * *
</PRE>
<P>pair_style coul/wolf 0.2 9.0
pair_coeff * *
</P>
<P><B>Description:</B>
</P>
<P>The <I>coul/cut</I> style computes the standard Coulombic interaction
potential given by
</P>
<CENTER><IMG SRC = "Eqs/pair_coulomb.jpg">
</CENTER>
<P>where C is an energy-conversion constant, Qi and Qj are the charges on
the 2 atoms, and epsilon is the dielectric constant which can be set
by the <A HREF = "dielectric.html">dielectric</A> command. The cutoff Rc truncates
the interaction distance.
</P>
<P>Style <I>coul/debye</I> adds an additional exp() damping factor to the
Coulombic term, given by
</P>
<CENTER><IMG SRC = "Eqs/pair_debye.jpg">
</CENTER>
<P>where kappa is the Debye length. This potential is another way to
mimic the screening effect of a polar solvent.
</P>
<P>Style <I>coul/wolf</I> computes Coulombic interactions via the Wolf
summation method, described in <A HREF = "#Wolf">Wolf</A>, given by:
</P>
<CENTER><IMG SRC = "Eqs/pair_coul_wolf.jpg">
</CENTER>
<P>where <I>alpha</I> is the damping parameter, and erc() and erfc() are
error-fuction and complementary error-function terms. This potential
is essentially a short-range, spherically-truncated,
charge-neutralized, shifted, pairwise <I>1/r</I> summation. With a
manipulation of adding and substracting a self term (for i = j) to the
first and second term on the right-hand-side, respectively, and a
small enough <I>alpha</I> damping parameter, the second term shrinks and
the potential becomes a rapidly-converging real-space summation. With
a long enough cutoff and small enough alpha parameter, the energy and
forces calcluated by the Wolf summation method approach those of the
Ewald sum. So it is a means of getting effective long-range
interactions with a short-range potential.
</P>
<P>Style <I>coul/long</I> computes the same Coulombic interactions as style
<I>coul/cut</I> except that an additional damping factor is applied so it
can be used in conjunction with the <A HREF = "kspace_style.html">kspace_style</A>
command and its <I>ewald</I> or <I>pppm</I> option. The Coulombic cutoff
specified for this style means that pairwise interactions within this
distance are computed directly; interactions outside that distance are
computed in reciprocal space.
</P>
<P>These potentials are designed to be combined with other pair
potentials via the <A HREF = "pair_hybrid.html">pair_style hybrid/overlay</A>
command. This is because they have no repulsive core. Hence if they
are used by themselves, there will be no repulsion to keep two
oppositely charged particles from overlapping each other.
</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>cutoff (distance units)
</UL>
<P>For <I>coul/cut</I> and <I>coul/debye</I>, the cutoff coefficient is optional.
If it is not used (as in some of the examples above), the default
global value specified in the pair_style command is used.
</P>
<P>For <I>coul/long</I> no cutoff can be specified for an individual I,J type
pair via the pair_coeff command. All type pairs use the same global
Coulombic cutoff specified in the pair_style command.
</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_6">-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 cutoff distance for the
<I>coul/cut</I> style can be mixed. The default mix value is <I>geometric</I>.
See the "pair_modify" command for details.
</P>
<P>The <A HREF = "pair_modify.html">pair_modify</A> shift option is not relevant
for these pair styles.
</P>
<P>The <I>coul/long</I> style supports the <A HREF = "pair_modify.html">pair_modify</A>
table option for tabulation of the short-range portion of the
long-range Coulombic interaction.
</P>
<P>These pair styles do not support the <A HREF = "pair_modify.html">pair_modify</A>
tail option for adding long-range tail corrections to energy and
pressure.
</P>
<P>These 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>This pair style can only be used via the <I>pair</I> keyword of the
<A HREF = "run_style.html">run_style respa</A> command. It does not support the
<I>inner</I>, <I>middle</I>, <I>outer</I> keywords.
</P>
<HR>
<P><B>Restrictions:</B>
</P>
<P>The <I>coul/long</I> style is part of the KSPACE package. It is only
enabled if LAMMPS was built with that package (which it is by
default). 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>, <A HREF = "pair_hybrid.html">pair_style
hybrid/overlay</A>
</P>
<P><B>Default:</B> none
</P>
<HR>
<A NAME = "Wolf"></A>
<P><B>(Wolf)</B> D. Wolf, P. Keblinski, S. R. Phillpot, J. Eggebrecht, J Chem
Phys, 110, 8254 (1999).
</P>
</HTML>
Event Timeline
Log In to Comment