Homec4science
Diffusion lammps (lammm-devel) Browse

lammps/doc/html/_sources/pair_meam_sw_spline.txt
caf9483a0a7clammm-devel

Last Change
Raw File

pair_meam_sw_spline.txt
View Options

pair_style meam/sw/spline
=========================
pair_style meam/sw/spline/omp
=============================
Syntax
""""""
.. parsed-literal::
pair_style meam/sw/spline
Examples
""""""""
.. parsed-literal::
pair_style meam/sw/spline
pair_coeff * * Ti.meam.sw.spline Ti
pair_coeff * * Ti.meam.sw.spline Ti Ti Ti
Description
"""""""""""
The *meam/sw/spline* style computes pairwise interactions for metals
using a variant of modified embedded-atom method (MEAM) potentials
:ref:`(Lenosky) <Lenosky>` with an additional Stillinger-Weber (SW) term
:ref:`(Stillinger) <Stillinger>` in the energy. This form of the potential
was first proposed by Nicklas, Fellinger, and Park
:ref:`(Nicklas) <Nicklas>`. We refer to it as MEAM+SW. The total energy E
is given by
.. image:: Eqs/pair_meam_sw_spline.jpg
:align: center
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
:doc:`pair_coeff <pair_coeff>` 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 :doc:`metal units <units>`.
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 :doc:`mass <mass>` 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
See the :doc:`pair_coeff <pair_coeff>` 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.
.. 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.
----------
**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 :doc:`pair_modify <pair_modify>`
shift, table, and tail options.
The *meam/sw/spline* pair style does not write its information to
:doc:`binary restart files <restart>`, 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 :doc:`run_style respa <run_style>` command. They do not
support the *inner*\ , *middle*\ , *outer* keywords.
----------
Restrictions
""""""""""""
This pair style requires the :doc:`newton <newton>` setting to be "on"
for pair interactions.
This pair style is only enabled if LAMMPS was built with the USER-MISC package.
See the :ref:`Making LAMMPS <start_3>` section for more info.
Related commands
""""""""""""""""
:doc:`pair_coeff <pair_coeff>`, :doc:`pair_style meam <pair_meam>`,
:doc:`pair_style meam/spline <pair_meam_spline>`
**Default:** none
----------
.. _Lenosky:
**(Lenosky)** Lenosky, Sadigh, Alonso, Bulatov, de la Rubia, Kim, Voter,
Kress, Modell. Simul. Mater. Sci. Eng. 8, 825 (2000).
.. _Stillinger:
**(Stillinger)** Stillinger, Weber, Phys. Rev. B 31, 5262 (1985).
.. _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.
.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Section_commands.html#comm
c4science · Help