forked from lijiext/lammps
138 lines
5.2 KiB
HTML
138 lines
5.2 KiB
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<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>
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</CENTER>
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<HR>
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<H3>pair_style meam/sw/spline
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</H3>
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<H3>pair_style meam/sw/spline/omp
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>pair_style meam/sw/spline
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</PRE>
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<P><B>Examples:</B>
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</P>
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<PRE>pair_style meam/sw/spline
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pair_coeff * * Ti.meam.sw.spline Ti
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pair_coeff * * Ti.meam.sw.spline Ti Ti Ti
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>The <I>meam/sw/spline</I> style computes pairwise interactions for metals
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using a variant of modified embedded-atom method (MEAM)
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potentials <A HREF = "#Lenosky">(Lenosky)</A> with an additional Stillinger-Weber (SW)
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term <A HREF = "#Stillinger">(Stillinger)</A> in the energy. This form of the
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potential was first proposed
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by Nicklas, Fellinger, and Park <A HREF = "#Nicklas">(Nicklas)</A>.
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We refer to it as MEAM+SW. The total energy E is given by
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</P>
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<CENTER><IMG SRC = "pair_meam_sw_spline.jpg">
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</CENTER>
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<P>where rho_I is the density at atom I, theta_JIK is the angle between
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atoms J, I, and K centered on atom I. The seven functions
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Phi, F, G, U, rho, f, and g are represented by cubic splines.
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</P>
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<P>The cutoffs and the coefficients for these spline functions are listed
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in a parameter file which is specified by the <A HREF = "pair_coeff.html">pair_coeff</A>
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command. Parameter files for different elements are
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included in the "potentials" directory of the LAMMPS distribution and
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have a ".meam.sw.spline" file suffix.
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All of these files are parameterized in terms of
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LAMMPS <A HREF = "units.html">metal units</A>.
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</P>
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<P>Note that unlike for other potentials, cutoffs for spline-based
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MEAM+SW potentials are not set in the pair_style or pair_coeff
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command; they are specified in the potential files themselves.
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</P>
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<P>Unlike the EAM pair style, which retrieves the atomic mass from
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the potential file, the spline-based MEAM+SW potentials do not include
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mass information; thus you need to use the <A HREF = "mass.html">mass</A>
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command to specify it.
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</P>
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<P>Only a single pair_coeff command is used with the meam/sw/spline style
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which specifies a potential file with parameters for all needed elements.
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These are mapped to LAMMPS atom types by specifying N additional arguments
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after the filename in the pair_coeff command, where N is the number of
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LAMMPS atom types:
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</P>
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<UL><LI>filename
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<LI>N element names = mapping of spline-based MEAM+SW elements to atom types
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</UL>
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<P>As an example, imagine the Ti.meam.sw.spline file has values for Ti.
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If your LAMMPS simulation has 3 atoms types and they are all to be
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treated with this potential, you would use the following pair_coeff command:
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</P>
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<P>pair_coeff * * Ti.meam.sw.spline Ti Ti Ti
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</P>
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<P>The 1st 2 arguments must be * * so as to span all LAMMPS atom types.
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The three Ti arguments map LAMMPS atom types 1,2,3 to the Ti element
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in the potential file. If a mapping value is specified as NULL, the
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mapping is not performed. This can be used when a <I>meam/sw/spline</I>
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potential is used as part of the hybrid pair style. The NULL values
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are placeholders for atom types that will be used with other potentials.
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</P>
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<P>IMPORTANT NOTE: The <I>meam/sw/spline</I> style currently supports only
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single-element MEAM+SW potentials. It may be extended for alloy systems
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in the future.
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</P>
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<HR>
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<P><B>Mixing, shift, table, tail correction, restart, rRESPA info</B>:
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</P>
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<P>The pair style does not support multiple element types or mixing.
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It has been designed for pure elements only.
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</P>
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<P>This pair style does not support the <A HREF = "pair_modify.html">pair_modify</A>
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shift, table, and tail options.
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</P>
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<P>The <I>meam/sw/spline</I> pair style does not write its information to
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<A HREF = "restart.html">binary restart files</A>, since it is stored in an external
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potential parameter file. Thus, you need to re-specify the pair_style
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and pair_coeff commands in an input script that reads a restart file.
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</P>
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<P>The <I>meam/sw/spline</I> pair style can only be used via the <I>pair</I> keyword of the
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<A HREF = "run_style.html">run_style respa</A> command. They do not support the
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<I>inner</I>, <I>middle</I>, <I>outer</I> keywords.
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</P>
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<HR>
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<P><B>Restrictions:</B>
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</P>
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<P>This pair style requires the <A HREF = "newton.html">newton</A> setting to be "on"
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for pair interactions.
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</P>
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<P>This pair style is only enabled if LAMMPS was built with the USER-MISC package.
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See the <A HREF = "Section_start.html#start_3">Making LAMMPS</A> section for more info.
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</P>
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<P><B>Related commands:</B>
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</P>
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<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>
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</P>
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<P><B>Default:</B> none
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</P>
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<HR>
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<A NAME = "Lenosky"></A>
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<P><B>(Lenosky)</B> Lenosky, Sadigh, Alonso, Bulatov, de la Rubia, Kim, Voter, Kress, Modell. Simul. Mater. Sci. Eng. 8, 825 (2000).
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</P>
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<A NAME = "Stillinger"></A>
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<P><B>(Stillinger)</B> Stillinger, Weber, Phys. Rev. B 31, 5262 (1985).
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</P>
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<A NAME = "Nicklas"></A>
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<P><B>(Nicklas)</B>
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The spline-based MEAM+SW format was first devised and used to develop
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potentials for bcc transition metals by Jeremy Nicklas, Michael Fellinger,
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and Hyoungki Park at The Ohio State University.
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</P>
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</HTML>
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