forked from lijiext/lammps
166 lines
5.0 KiB
Plaintext
166 lines
5.0 KiB
Plaintext
pair_style meam/sw/spline
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=========================
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pair_style meam/sw/spline/omp
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=============================
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Syntax
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""""""
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.. parsed-literal::
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pair_style meam/sw/spline
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Examples
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""""""""
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.. parsed-literal::
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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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Description
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"""""""""""
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The *meam/sw/spline* style computes pairwise interactions for metals
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using a variant of modified embedded-atom method (MEAM) potentials
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:ref:`(Lenosky) <Lenosky>` with an additional Stillinger-Weber (SW) term
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:ref:`(Stillinger) <Stillinger>` in the energy. This form of the potential
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was first proposed by Nicklas, Fellinger, and Park
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:ref:`(Nicklas) <Nicklas>`. We refer to it as MEAM+SW. The total energy E
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is given by
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.. image:: Eqs/pair_meam_sw_spline.jpg
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:align: center
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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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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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:doc:`pair_coeff <pair_coeff>` 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.sw.spline" file suffix. All of these
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files are parameterized in terms of LAMMPS :doc:`metal units <units>`.
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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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Unlike the EAM pair style, which retrieves the atomic mass from the
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potential file, the spline-based MEAM+SW potentials do not include
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mass information; thus you need to use the :doc:`mass <mass>` command to
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specify it.
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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
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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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* filename
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* N element names = mapping of spline-based MEAM+SW elements to atom types
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See the :doc:`pair_coeff <pair_coeff>` doc page for alternate ways
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to specify the path for the potential file.
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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
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command:
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pair_coeff * * Ti.meam.sw.spline Ti Ti Ti
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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 *meam/sw/spline*
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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
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potentials.
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.. note::
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The *meam/sw/spline* style currently supports only
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single-element MEAM+SW potentials. It may be extended for alloy
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systems in the future.
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Example input scripts that use this pair style are provided
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in the examples/USER/misc/meam_sw_spline directory.
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----------
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**Mixing, shift, table, tail correction, restart, rRESPA info**\ :
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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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This pair style does not support the :doc:`pair_modify <pair_modify>`
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shift, table, and tail options.
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The *meam/sw/spline* pair style does not write its information to
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:doc:`binary restart files <restart>`, 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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The *meam/sw/spline* pair style can only be used via the *pair*
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keyword of the :doc:`run_style respa <run_style>` command. They do not
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support the *inner*\ , *middle*\ , *outer* keywords.
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----------
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Restrictions
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""""""""""""
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This pair style requires the :doc:`newton <newton>` setting to be "on"
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for pair interactions.
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This pair style is only enabled if LAMMPS was built with the USER-MISC package.
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See the :ref:`Making LAMMPS <start_3>` section for more info.
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Related commands
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""""""""""""""""
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:doc:`pair_coeff <pair_coeff>`, :doc:`pair_style meam <pair_meam>`,
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:doc:`pair_style meam/spline <pair_meam_spline>`
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**Default:** none
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----------
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.. _Lenosky:
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**(Lenosky)** Lenosky, Sadigh, Alonso, Bulatov, de la Rubia, Kim, Voter,
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Kress, Modell. Simul. Mater. Sci. Eng. 8, 825 (2000).
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.. _Stillinger:
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**(Stillinger)** Stillinger, Weber, Phys. Rev. B 31, 5262 (1985).
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.. _Nicklas:
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**(Nicklas)**
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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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.. _lws: http://lammps.sandia.gov
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.. _ld: Manual.html
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.. _lc: Section_commands.html#comm
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