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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 gauss command
</H3>
<H3>pair_style gauss/gpu command
</H3>
<H3>pair_style gauss/omp command
</H3>
<H3>pair_style gauss/cut command
</H3>
<H3>pair_style gauss/cut/omp command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>pair_style gauss cutoff
pair_style gauss/cut cutoff
</PRE>
<UL><LI>cutoff = global cutoff for Gauss interactions (distance units)
</UL>
<P><B>Examples:</B>
</P>
<PRE>pair_style gauss 12.0
pair_coeff * * 1.0 0.9
pair_coeff 1 4 1.0 0.9 10.0
</PRE>
<PRE>pair_style gauss/cut 3.5
pair_coeff 1 4 0.2805 1.45 0.112
</PRE>
<P><B>Description:</B>
</P>
<P>Style <I>gauss</I> computes a tethering potential of the form
</P>
<CENTER><IMG SRC = "Eqs/pair_gauss.jpg">
</CENTER>
<P>between an atom and its corresponding tether site which will typically
be a frozen atom in the simulation. Rc is the cutoff.
</P>
<P>The following coefficients must be defined for each pair of atom 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>B (1/distance^2 units)
<LI>cutoff (distance units)
</UL>
<P>The last coefficient is optional. If not specified, the global cutoff
is used.
</P>
<P>Style <I>gauss/cut</I> computes a generalized Gaussian interaction potential
between pairs of particles:
</P>
<CENTER><IMG SRC = "Eqs/pair_gauss_cut.jpg">
</CENTER>
<P>where H determines together with the standard deviation sigma_h the
peak height of the Gaussian function, and r_mh the peak position.
Examples of the use of the Gaussian potentials include implicit
solvent simulations of salt ions <A HREF = "#Lenart">(Lenart)</A> and of surfactants
<A HREF = "#Jusufi">(Jusufi)</A>. In these instances the Gaussian potential mimics
the hydration barrier between a pair of particles. The hydration
barrier is located at r_mh and has a width of sigma_h. The prefactor
determines the hight of the potential barrier.
</P>
<P>The following coefficients must be defined for each pair of atom types
via the <A HREF = "pair_coeff.html">pair_coeff</A> command as in the example 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>H (energy * distance units)
<LI>r_mh (distance units)
<LI>sigma_h (distance units)
</UL>
<P>The global cutoff (r_c) specified in the pair_style command is used.
</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 "-suffix command-line
switch7_Section_start.html#start_6 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>These pair styles do not support mixing. Thus, coefficients for all
I,J pairs must be specified explicitly.
</P>
<P>The <I>gauss</I> style does not support the <A HREF = "pair_modify.html">pair_modify</A>
shift option. There is no effect due to the Gaussian well beyond the
cutoff; hence reasonable cutoffs need to be specified.
</P>
<P>The <I>gauss/cut</I> style supports the <A HREF = "pair_modify.html">pair_modify</A> shift
option for the energy of the Gauss-potential portion of the pair
interaction.
</P>
<P>The <A HREF = "pair_modify.html">pair_modify</A> table and tail options are not
relevant for these pair styles.
</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>These 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>The <I>gauss</I> pair style tallies an "occupancy" count of how many Gaussian-well
sites have an atom within the distance at which the force is a maximum
= sqrt(0.5/b). This quantity can be accessed via the <A HREF = "compute_pair.html">compute
pair</A> command as a vector of values of length 1.
</P>
<P>To print this quantity to the log file (with a descriptive column
heading) the following commands could be included in an input script:
</P>
<PRE>compute gauss all pair gauss
variable occ equal c_gauss[1]
thermo_style custom step temp epair v_occ
</PRE>
<HR>
<P><B>Restrictions:</B>
</P>
<P>The <I>gauss/cut</I> style is part of the "user-misc" package. It is only
enabled if LAMMPS is build with that package. See the <A HREF = "Section_start.html#3">Making of
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_coul_diel.html">pair_style coul/diel</A>
</P>
<P><B>Default:</B> none
</P>
<A NAME = "Lenart"></A>
<P><B>(Lenart)</B> Lenart , Jusufi, and Panagiotopoulos, J Chem Phys, 126,
044509 (2007).
</P>
<A NAME = "Jusufi"></A>
<P><B>(Jusufi)</B> Jusufi, Hynninen, and Panagiotopoulos, J Phys Chem B, 112,
13783 (2008).
</P>
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