forked from lijiext/lammps
152 lines
5.8 KiB
HTML
152 lines
5.8 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 meam/spline
|
|
</H3>
|
|
<H3>pair_style meam/spline/omp
|
|
</H3>
|
|
<P><B>Syntax:</B>
|
|
</P>
|
|
<PRE>pair_style meam/spline
|
|
</PRE>
|
|
<P><B>Examples:</B>
|
|
</P>
|
|
<PRE>pair_style meam/spline
|
|
pair_coeff * * Ti.meam.spline Ti
|
|
pair_coeff * * Ti.meam.spline Ti Ti Ti
|
|
</PRE>
|
|
<P><B>Description:</B>
|
|
</P>
|
|
<P>The <I>meam/spline</I> style computes pairwise interactions for metals
|
|
using a variant of modified embedded-atom method (MEAM) potentials
|
|
<A HREF = "#Lenosky">(Lenosky)</A>. The total energy E is given by
|
|
</P>
|
|
<CENTER><IMG SRC = "Eqs/pair_meam_spline.jpg">
|
|
</CENTER>
|
|
<P>where rho_i is the density at atom I, theta_jik is the angle between
|
|
atoms J, I, and K centered on atom I. The five functions Phi, U, rho,
|
|
f, and g are represented by cubic splines.
|
|
</P>
|
|
<P>The cutoffs and the coefficients for these spline functions are listed
|
|
in a parameter file which is specified by the
|
|
<A HREF = "pair_coeff.html">pair_coeff</A> command. Parameter files for different
|
|
elements are included in the "potentials" directory of the LAMMPS
|
|
distribution and have a ".meam.spline" file suffix. All of these
|
|
files are parameterized in terms of LAMMPS <A HREF = "units.html">metal units</A>.
|
|
</P>
|
|
<P>Note that unlike for other potentials, cutoffs for spline-based MEAM
|
|
potentials are not set in the pair_style or pair_coeff command; they
|
|
are specified in the potential files themselves.
|
|
</P>
|
|
<P>Unlike the EAM pair style, which retrieves the atomic mass from the
|
|
potential file, the spline-based MEAM potentials do not include mass
|
|
information; thus you need to use the <A HREF = "mass.html">mass</A> command to
|
|
specify it.
|
|
</P>
|
|
<P>Only a single pair_coeff command is used with the <I>meam/spline</I> style
|
|
which specifies a potential file with parameters for all needed
|
|
elements. These are mapped to LAMMPS atom types by specifying N
|
|
additional arguments after the filename in the pair_coeff command,
|
|
where N is the number of LAMMPS atom types:
|
|
</P>
|
|
<UL><LI>filename
|
|
<LI>N element names = mapping of spline-based MEAM elements to atom types
|
|
</UL>
|
|
<P>See the <A HREF = "pair_coeff.html">pair_coeff</A> doc page for alternate ways
|
|
to specify the path for the potential file.
|
|
</P>
|
|
<P>As an example, imagine the Ti.meam.spline file has values for Ti. If
|
|
your LAMMPS simulation has 3 atoms types and they are all to be
|
|
treated with this potentials, you would use the following pair_coeff
|
|
command:
|
|
</P>
|
|
<PRE>pair_coeff * * Ti.meam.spline Ti Ti Ti
|
|
</PRE>
|
|
<P>The 1st 2 arguments must be * * so as to span all LAMMPS atom types.
|
|
The three Ti arguments map LAMMPS atom types 1,2,3 to the Ti element
|
|
in the potential file. If a mapping value is specified as NULL, the
|
|
mapping is not performed. This can be used when a <I>meam/spline</I>
|
|
potential is used as part of the <I>hybrid</I> pair style. The NULL values
|
|
are placeholders for atom types that will be used with other
|
|
potentials.
|
|
</P>
|
|
<P>IMPORTANT NOTE: The <I>meam/spline</I> style currently supports only
|
|
single-element MEAM potentials. It may be extended for alloy systems
|
|
in the future.
|
|
</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>The current version of this pair style does not support multiple
|
|
element types or mixing. It has been designed for pure elements only.
|
|
</P>
|
|
<P>This pair style does not support the <A HREF = "pair_modify.html">pair_modify</A>
|
|
shift, table, and tail options.
|
|
</P>
|
|
<P>The <I>meam/spline</I> pair style does not write its information to <A HREF = "restart.html">binary
|
|
restart files</A>, since it is stored in an external
|
|
potential parameter file. Thus, you need to re-specify the pair_style
|
|
and pair_coeff commands in an input script that reads a restart file.
|
|
</P>
|
|
<P>The <I>meam/spline</I> pair style 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>
|
|
<HR>
|
|
|
|
<P><B>Restrictions:</B>
|
|
</P>
|
|
<P>This pair style requires the <A HREF = "newton.html">newton</A> setting to be "on"
|
|
for pair interactions.
|
|
</P>
|
|
<P>This pair style is only enabled if LAMMPS was built with the USER-MISC
|
|
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>, <A HREF = "pair_meam.html">pair_style meam</A>
|
|
</P>
|
|
<P><B>Default:</B> none
|
|
</P>
|
|
<HR>
|
|
|
|
<A NAME = "Lenosky"></A>
|
|
|
|
<P><B>(Lenosky)</B> Lenosky, Sadigh, Alonso, Bulatov, de la Rubia, Kim, Voter,
|
|
Kress, Modelling Simulation Materials Science Enginerring, 8, 825
|
|
(2000).
|
|
</P>
|
|
</HTML>
|