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rLAMMPS lammps
pair_meam_sw_spline.html
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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 meam/sw/spline
</H3>
<H3>pair_style meam/sw/spline/omp
</H3>
<P><B>Syntax:</B>
</P>
<PRE>pair_style meam/sw/spline
</PRE>
<P><B>Examples:</B>
</P>
<PRE>pair_style meam/sw/spline
pair_coeff * * Ti.meam.sw.spline Ti
pair_coeff * * Ti.meam.sw.spline Ti Ti Ti
</PRE>
<P><B>Description:</B>
</P>
<P>The <I>meam/sw/spline</I> style computes pairwise interactions for metals
using a variant of modified embedded-atom method (MEAM) potentials
<A HREF = "#Lenosky">(Lenosky)</A> with an additional Stillinger-Weber (SW) term
<A HREF = "#Stillinger">(Stillinger)</A> in the energy. This form of the potential
was first proposed by Nicklas, Fellinger, and Park
<A HREF = "#Nicklas">(Nicklas)</A>. We refer to it as MEAM+SW. The total energy E
is given by
</P>
<CENTER><IMG SRC = "Eqs/pair_meam_sw_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 seven functions
Phi, F, G, 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.sw.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+SW 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+SW 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 meam/sw/spline 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+SW 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.sw.spline file has values for Ti.
If your LAMMPS simulation has 3 atoms types and they are all to be
treated with this potential, you would use the following pair_coeff
command:
</P>
<P>pair_coeff * * Ti.meam.sw.spline Ti Ti Ti
</P>
<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/sw/spline</I>
potential is used as part of the hybrid pair style. The NULL values
are placeholders for atom types that will be used with other
potentials.
</P>
<P>IMPORTANT NOTE: The <I>meam/sw/spline</I> style currently supports only
single-element MEAM+SW potentials. It may be extended for alloy
systems in the future.
</P>
<P>Example input scripts that use this pair style are provided
in the examples/USER/misc/meam_sw_spline directory.
</P>
<HR>
<P><B>Mixing, shift, table, tail correction, restart, rRESPA info</B>:
</P>
<P>The 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/sw/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/sw/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>,
<A HREF = "pair_meam_spline.html">pair_style meam/spline</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, Modell. Simul. Mater. Sci. Eng. 8, 825 (2000).
</P>
<A NAME = "Stillinger"></A>
<P><B>(Stillinger)</B> Stillinger, Weber, Phys. Rev. B 31, 5262 (1985).
</P>
<A NAME = "Nicklas"></A>
<P><B>(Nicklas)</B>
The spline-based MEAM+SW format was first devised and used to develop
potentials for bcc transition metals by Jeremy Nicklas, Michael Fellinger,
and Hyoungki Park at The Ohio State University.
</P>
</HTML>
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