forked from lijiext/lammps
153 lines
5.9 KiB
HTML
153 lines
5.9 KiB
HTML
<HTML>
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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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<HR>
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<H3>pair_style meam/spline
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</H3>
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<H3>pair_style meam/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/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/spline
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pair_coeff * * Ti.meam.spline Ti
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pair_coeff * * Ti.meam.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/spline</I> style computes pairwise interactions for metals
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using a variant of modified embedded-atom method (MEAM) potentials
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<A HREF = "#Lenosky">(Lenosky)</A>. The total energy E is given by
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</P>
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<CENTER><IMG SRC = "Eqs/pair_meam_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 five functions Phi, U, rho,
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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
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<A HREF = "pair_coeff.html">pair_coeff</A> command. Parameter files for different
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elements are included in the "potentials" directory of the LAMMPS
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distribution and have a ".meam.spline" file suffix. All of these
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files are parameterized in terms of 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 MEAM
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potentials are not set in the pair_style or pair_coeff command; they
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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 the
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potential file, the spline-based MEAM potentials do not include mass
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information; thus you need to use the <A HREF = "mass.html">mass</A> command to
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specify it.
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</P>
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<P>Only a single pair_coeff command is used with the <I>meam/spline</I> style
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which specifies a potential file with parameters for all needed
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elements. These are mapped to LAMMPS atom types by specifying N
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additional arguments after the filename in the pair_coeff command,
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where N is the number of 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 elements to atom types
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</UL>
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<P>See the <A HREF = "pair_coeff.html">pair_coeff</A> doc page for alternate ways
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to specify the path for the potential file.
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</P>
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<P>As an example, imagine the Ti.meam.spline file has values for Ti. If
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your LAMMPS simulation has 3 atoms types and they are all to be
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treated with this potentials, you would use the following pair_coeff
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command:
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</P>
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<PRE>pair_coeff * * Ti.meam.spline Ti Ti Ti
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</PRE>
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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/spline</I>
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potential is used as part of the <I>hybrid</I> pair style. The NULL values
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are placeholders for atom types that will be used with other
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potentials.
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</P>
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<P>IMPORTANT NOTE: The <I>meam/spline</I> style currently supports only
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single-element MEAM 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>Styles with a <I>cuda</I>, <I>gpu</I>, <I>intel</I>, <I>kk</I>, <I>omp</I>, or <I>opt</I> suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed in <A HREF = "Section_accelerate.html">Section_accelerate</A>
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of the manual. The accelerated styles take the same arguments and
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should produce the same results, except for round-off and precision
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issues.
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</P>
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<P>These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
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KOKKOS, USER-OMP and OPT packages, respectively. They are only
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enabled if LAMMPS was built with those packages. See the <A HREF = "Section_start.html#start_3">Making
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LAMMPS</A> section for more info.
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</P>
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<P>You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the <A HREF = "Section_start.html#start_7">-suffix command-line
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switch</A> when you invoke LAMMPS, or you can
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use the <A HREF = "suffix.html">suffix</A> command in your input script.
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</P>
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<P>See <A HREF = "Section_accelerate.html">Section_accelerate</A> of the manual for
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more instructions on how to use the accelerated styles effectively.
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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 current version of this pair style does not support multiple
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element types or mixing. 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/spline</I> pair style does not write its information to <A HREF = "restart.html">binary
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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/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
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package. See the <A HREF = "Section_start.html#start_3">Making LAMMPS</A> section
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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>
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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,
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Kress, Modelling Simulation Materials Science Enginerring, 8, 825
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(2000).
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</P>
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</HTML>
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