98 lines
2.9 KiB
ReStructuredText
98 lines
2.9 KiB
ReStructuredText
.. index:: pair_style pod
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pair_style pod command
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========================
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Syntax
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""""""
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.. code-block:: LAMMPS
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pair_style pod
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Examples
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""""""""
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.. code-block:: LAMMPS
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pair_style pod
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pair_coeff * * Ta_param.pod Ta_coefficients.pod Ta
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Description
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"""""""""""
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.. versionadded:: 22Dec2022
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Pair style *pod* defines the proper orthogonal descriptor (POD)
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potential :ref:`(Nguyen) <Nguyen20221>`. The mathematical definition of
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the POD potential is described from :doc:`fitpod <fitpod_command>`, which is
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used to fit the POD potential to *ab initio* energy and force data.
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Only a single pair_coeff command is used with the *pod* style which
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specifies a POD parameter file followed by a coefficient file.
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The coefficient file (``Ta_coefficients.pod``) contains coefficients for the
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POD potential. The top of the coefficient file can contain any number of
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blank and comment lines (start with #), but follows a strict format
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after that. The first non-blank non-comment line must contain:
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* POD_coefficients: *ncoeff*
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This is followed by *ncoeff* coefficients, one per line. The coefficient
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file is generated after training the POD potential using :doc:`fitpod
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<fitpod_command>`.
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The POD parameter file (``Ta_param.pod``) can contain blank and comment lines
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(start with #) anywhere. Each non-blank non-comment line must contain
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one keyword/value pair. See :doc:`fitpod <fitpod_command>` for the description
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of all the keywords that can be assigned in the parameter file.
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As an example, if a LAMMPS indium phosphide simulation has 4 atoms
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types, with the first two being indium and the third and fourth being
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phophorous, the pair_coeff command would look like this:
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.. code-block:: LAMMPS
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pair_coeff * * pod InP_param.pod InP_coefficients.pod In In P P
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The first 2 arguments must be \* \* so as to span all LAMMPS atom types.
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The two filenames are for the parameter and coefficient files, respectively.
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The two trailing 'In' arguments map LAMMPS atom types 1 and 2 to the
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POD 'In' element. The two trailing 'P' arguments map LAMMPS atom types
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3 and 4 to the POD 'P' element.
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If a POD mapping value is specified as NULL, the mapping is not
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performed. This can be used when a *pod* potential is used as part of
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the *hybrid* pair style. The NULL values are placeholders for atom
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types that will be used with other potentials.
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Examples about training and using POD potentials are found in the
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directory lammps/examples/PACKAGES/pod.
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----------
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Restrictions
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""""""""""""
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This style is part of the ML-POD package. It is only enabled if LAMMPS
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was built with that package. See the :doc:`Build package
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<Build_package>` page for more info.
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This pair style does not compute per-atom energies and per-atom stresses.
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Related commands
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""""""""""""""""
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:doc:`fitpod <fitpod_command>`,
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Default
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"""""""
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none
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----------
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.. _Nguyen20221:
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**(Nguyen)** Nguyen and Rohskopf, arXiv preprint arXiv:2209.02362 (2022).
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