lammps/doc/pair_meam_sw_spline.txt

"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)

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pair_style meam/sw/spline :h3
pair_style meam/sw/spline/omp :h3

[Syntax:]

pair_style meam/sw/spline :pre

[Examples:]

pair_style meam/sw/spline
pair_coeff * * Ti.meam.sw.spline Ti
pair_coeff * * Ti.meam.sw.spline Ti Ti Ti :pre

[Description:]

The {meam/sw/spline} style computes pairwise interactions for metals
using a variant of modified embedded-atom method (MEAM) potentials
"(Lenosky)"_#Lenosky with an additional Stillinger-Weber (SW) term
"(Stillinger)"_#Stillinger in the energy.  This form of the potential
was first proposed by Nicklas, Fellinger, and Park
"(Nicklas)"_#Nicklas.  We refer to it as MEAM+SW.  The total energy E
is given by

:c,image(Eqs/pair_meam_sw_spline.jpg)

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.

The cutoffs and the coefficients for these spline functions are listed
in a parameter file which is specified by the
"pair_coeff"_pair_coeff.html 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 "metal units"_units.html.

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.

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 "mass"_mass.html command to
specify it.

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:

filename
N element names = mapping of spline-based MEAM+SW elements to atom types :ul

See the "pair_coeff"_pair_coeff.html doc page for alternate ways
to specify the path for the potential file.

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:

pair_coeff * * Ti.meam.sw.spline Ti Ti Ti

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 {meam/sw/spline}
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.

IMPORTANT NOTE: The {meam/sw/spline} style currently supports only
single-element MEAM+SW potentials.  It may be extended for alloy
systems in the future.

Example input scripts that use this pair style are provided
in the examples/USER/misc/meam_sw_spline directory.

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[Mixing, shift, table, tail correction, restart, rRESPA info]:

The pair style does not support multiple element types or mixing. 
It has been designed for pure elements only.

This pair style does not support the "pair_modify"_pair_modify.html
shift, table, and tail options.

The {meam/sw/spline} pair style does not write its information to
"binary restart files"_restart.html, 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.

The {meam/sw/spline} pair style can only be used via the {pair}
keyword of the "run_style respa"_run_style.html command.  They do not
support the {inner}, {middle}, {outer} keywords.

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[Restrictions:]

This pair style requires the "newton"_newton.html setting to be "on"
for pair interactions.

This pair style is only enabled if LAMMPS was built with the USER-MISC package.
See the "Making LAMMPS"_Section_start.html#start_3 section for more info.

[Related commands:]

"pair_coeff"_pair_coeff.html, "pair_style meam"_pair_meam.html,
"pair_style meam/spline"_pair_meam_spline.html

[Default:] none

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:link(Lenosky)
[(Lenosky)] Lenosky, Sadigh, Alonso, Bulatov, de la Rubia, Kim, Voter,
Kress, Modell. Simul. Mater. Sci. Eng. 8, 825 (2000).

:link(Stillinger)
[(Stillinger)] Stillinger, Weber, Phys. Rev. B 31, 5262 (1985).

:link(Nicklas)
[(Nicklas)] 
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.