forked from lijiext/lammps
283 lines
10 KiB
HTML
283 lines
10 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 coul/cut command
|
|
</H3>
|
|
<H3>pair_style coul/cut/gpu command
|
|
</H3>
|
|
<H3>pair_style coul/cut/omp command
|
|
</H3>
|
|
<H3>pair_style coul/debye command
|
|
</H3>
|
|
<H3>pair_style coul/debye/gpu command
|
|
</H3>
|
|
<H3>pair_style coul/debye/omp command
|
|
</H3>
|
|
<H3>pair_style coul/dsf command
|
|
</H3>
|
|
<H3>pair_style coul/dsf/gpu command
|
|
</H3>
|
|
<H3>pair_style coul/dsf/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/msm command
|
|
</H3>
|
|
<H3>pair_style coul/msm/omp command
|
|
</H3>
|
|
<H3>pair_style coul/wolf command
|
|
</H3>
|
|
<H3>pair_style coul/wolf/omp command
|
|
</H3>
|
|
<H3>pair_style tip4p/cut command
|
|
</H3>
|
|
<H3>pair_style tip4p/long command
|
|
</H3>
|
|
<H3>pair_style tip4p/cut/omp command
|
|
</H3>
|
|
<H3>pair_style tip4p/long/omp command
|
|
</H3>
|
|
<P><B>Syntax:</B>
|
|
</P>
|
|
<PRE>pair_style coul/cut cutoff
|
|
pair_style coul/debye kappa cutoff
|
|
pair_style coul/dsf alpha cutoff
|
|
pair_style coul/long cutoff
|
|
pair_style coul/long/gpu cutoff
|
|
pair_style coul/wolf alpha cutoff
|
|
pair_style tip4p/cut otype htype btype atype qdist cutoff
|
|
pair_style tip4p/long otype htype btype atype qdist 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/dsf 0.05 10.0
|
|
pair_coeff * *
|
|
</PRE>
|
|
<PRE>pair_style coul/long 10.0
|
|
pair_coeff * *
|
|
</PRE>
|
|
<PRE>pair_style coul/msm 10.0
|
|
pair_coeff * *
|
|
</PRE>
|
|
<PRE>pair_style coul/wolf 0.2 9.0
|
|
pair_coeff * *
|
|
</PRE>
|
|
<PRE>pair_style tip4p/cut 1 2 7 8 0.15 12.0
|
|
pair_coeff * *
|
|
</PRE>
|
|
<PRE>pair_style tip4p/long 1 2 7 8 0.15 10.0
|
|
pair_coeff * *
|
|
</PRE>
|
|
<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/dsf</I> computes Coulombic interactions via the damped
|
|
shifted force model described in <A HREF = "#Fennell">Fennell</A>, given by:
|
|
</P>
|
|
<CENTER><IMG SRC = "Eqs/pair_coul_dsf.jpg">
|
|
</CENTER>
|
|
<P>where <I>alpha</I> is the damping parameter and erfc() is the
|
|
complementary error-function. The potential corrects issues in the
|
|
Wolf model (described below) to provide consistent forces and energies
|
|
(the Wolf potential is not differentiable at the cutoff) and smooth
|
|
decay to zero.
|
|
</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>Styles <I>coul/long</I> and <I>coul/msm</I> compute 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>Styles <I>tip4p/cut</I> and <I>tip4p/long</I> implement the coulomb part of
|
|
the TIP4P water model of <A HREF = "#Jorgensen">(Jorgensen)</A>, which introduces
|
|
a massless site located a short distance away from the oxygen atom
|
|
along the bisector of the HOH angle. The atomic types of the oxygen and
|
|
hydrogen atoms, the bond and angle types for OH and HOH interactions,
|
|
and the distance to the massless charge site are specified as
|
|
pair_style arguments. Style <I>tip4p/cut</I> uses a global cutoff for
|
|
Coulomb interactions; style <I>tip4p/long</I> is for use with a long-range
|
|
Coulombic solver (Ewald or PPPM).
|
|
</P>
|
|
<P>IMPORTANT NOTE: For each TIP4P water molecule in your system, the atom
|
|
IDs for the O and 2 H atoms must be consecutive, with the O atom
|
|
first. This is to enable LAMMPS to "find" the 2 H atoms associated
|
|
with each O atom. For example, if the atom ID of an O atom in a TIP4P
|
|
water molecule is 500, then its 2 H atoms must have IDs 501 and 502.
|
|
</P>
|
|
<P>See the <A HREF = "Section_howto.html#howto_8">howto section</A> for more
|
|
information on how to use the TIP4P pair styles and lists of
|
|
parameters to set. Note that the neighobr list cutoff for Coulomb
|
|
interactions is effectively extended by a distance 2*qdist when using
|
|
the TIP4P pair style, to account for the offset distance of the
|
|
fictitious charges on O atoms in water molecules. Thus it is
|
|
typically best in an efficiency sense to use a LJ cutoff >= Coulomb
|
|
cutoff + 2*qdist, to shrink the size of the neighbor list. This leads
|
|
to slightly larger cost for the long-range calculation, so you can
|
|
test the trade-off for your model.
|
|
</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> and <I>coul/msm</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>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 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>, <I>coul/msm</I> and <I>tip4p/long</I> styles are part of the
|
|
KSPACE package. They are 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>
|
|
<A HREF = "kspace_style.html">kspace_style</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>
|
|
<A NAME = "Fennell"></A>
|
|
|
|
<P><B>(Fennell)</B> C. J. Fennell, J. D. Gezelter, J Chem Phys, 124,
|
|
234104 (2006).
|
|
</P>
|
|
</HTML>
|