forked from lijiext/lammps
188 lines
5.7 KiB
Plaintext
188 lines
5.7 KiB
Plaintext
.. index:: pair_style edip
|
|
|
|
pair_style edip command
|
|
=======================
|
|
|
|
Syntax
|
|
""""""
|
|
|
|
.. parsed-literal::
|
|
|
|
pair_style edip
|
|
|
|
.. parsed-literal::
|
|
|
|
pair_style edip/omp
|
|
|
|
Examples
|
|
""""""""
|
|
|
|
pair_style edip
|
|
pair_coeff * * Si.edip Si
|
|
|
|
Description
|
|
"""""""""""
|
|
|
|
The *edip* style computes a 3-body :ref:`EDIP <EDIP>` potential which is
|
|
popular for modeling silicon materials where it can have advantages
|
|
over other models such as the :doc:`Stillinger-Weber <pair_sw>` or
|
|
:doc:`Tersoff <pair_tersoff>` potentials. In EDIP, the energy E of a
|
|
system of atoms is
|
|
|
|
.. image:: Eqs/pair_edip.jpg
|
|
:align: center
|
|
|
|
where phi2 is a two-body term and phi3 is a three-body term. The
|
|
summations in the formula are over all neighbors J and K of atom I
|
|
within a cutoff distance = a.
|
|
Both terms depend on the local environment of atom I through its
|
|
effective coordination number defined by Z, which is unity for a
|
|
cutoff distance < c and gently goes to 0 at distance = a.
|
|
|
|
Only a single pair_coeff command is used with the *edip* style which
|
|
specifies a EDIP 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 EDIP 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 a file Si.edip has EDIP values for Si.
|
|
|
|
EDIP files in the *potentials* directory of the LAMMPS
|
|
distribution have a ".edip" suffix. Lines that are not blank or
|
|
comments (starting with #) define parameters for a triplet of
|
|
elements. The parameters in a single entry correspond to the two-body
|
|
and three-body coefficients in the formula above:
|
|
|
|
* element 1 (the center atom in a 3-body interaction)
|
|
* element 2
|
|
* element 3
|
|
* A (energy units)
|
|
* B (distance units)
|
|
* cutoffA (distance units)
|
|
* cutoffC (distance units)
|
|
* alpha
|
|
* beta
|
|
* eta
|
|
* gamma (distance units)
|
|
* lambda (energy units)
|
|
* mu
|
|
* tho
|
|
* sigma (distance units)
|
|
* Q0
|
|
* u1
|
|
* u2
|
|
* u3
|
|
* u4
|
|
|
|
The A, B, beta, sigma parameters are used only for two-body interactions.
|
|
The eta, gamma, lambda, mu, Q0 and all u1 to u4 parameters are used only
|
|
for three-body interactions. The alpha and cutoffC parameters are used
|
|
for the coordination environment function only.
|
|
|
|
The EDIP potential file must contain entries for all the
|
|
elements listed in the pair_coeff command. It can also contain
|
|
entries for additional elements not being used in a particular
|
|
simulation; LAMMPS ignores those entries.
|
|
|
|
For a single-element simulation, only a single entry is required
|
|
(e.g. SiSiSi). For a two-element simulation, the file must contain 8
|
|
entries (for SiSiSi, SiSiC, SiCSi, SiCC, CSiSi, CSiC, CCSi, CCC), that
|
|
specify EDIP parameters for all permutations of the two elements
|
|
interacting in three-body configurations. Thus for 3 elements, 27
|
|
entries would be required, etc.
|
|
|
|
At the moment, only a single element parametrization is
|
|
implemented. However, the author is not aware of other
|
|
multi-element EDIP parametrizations. If you know any and
|
|
you are interest in that, please contact the author of
|
|
the EDIP package.
|
|
|
|
|
|
----------
|
|
|
|
|
|
Styles with a *gpu*\ , *intel*\ , *kk*\ , *omp*\ , or *opt* suffix are
|
|
functionally the same as the corresponding style without the suffix.
|
|
They have been optimized to run faster, depending on your available
|
|
hardware, as discussed in :doc:`Section_accelerate <Section_accelerate>`
|
|
of the manual. The accelerated styles take the same arguments and
|
|
should produce the same results, except for round-off and precision
|
|
issues.
|
|
|
|
These accelerated styles are part of the GPU, USER-INTEL, KOKKOS,
|
|
USER-OMP and OPT packages, respectively. They are only enabled if
|
|
LAMMPS was built with those packages. See the :ref:`Making LAMMPS <start_3>` section for more info.
|
|
|
|
You can specify the accelerated styles explicitly in your input script
|
|
by including their suffix, or you can use the :ref:`-suffix command-line switch <start_7>` when you invoke LAMMPS, or you can
|
|
use the :doc:`suffix <suffix>` command in your input script.
|
|
|
|
See :doc:`Section_accelerate <Section_accelerate>` of the manual for
|
|
more instructions on how to use the accelerated styles effectively.
|
|
|
|
|
|
----------
|
|
|
|
|
|
**Mixing, shift, table, tail correction, restart, rRESPA info**\ :
|
|
|
|
This pair style does not support the :doc:`pair_modify <pair_modify>`
|
|
shift, table, and tail options.
|
|
|
|
This pair style does not write its information to :doc:`binary restart files <restart>`, since it is stored in potential files. Thus, you
|
|
need to re-specify the pair_style and pair_coeff commands in an input
|
|
script that reads a restart file.
|
|
|
|
This pair style can only be used via the *pair* keyword of the
|
|
:doc:`run_style respa <run_style>` command. It does not support the
|
|
*inner*\ , *middle*\ , *outer* keywords.
|
|
|
|
|
|
----------
|
|
|
|
|
|
Restrictions
|
|
""""""""""""
|
|
|
|
|
|
This angle style can only be used if LAMMPS was built with the
|
|
USER-MISC package. See the :ref:`Making LAMMPS <start_3>`
|
|
section for more info on packages.
|
|
|
|
This pair style requires the :doc:`newton <newton>` setting to be "on"
|
|
for pair interactions.
|
|
|
|
The EDIP potential files provided with LAMMPS (see the potentials directory)
|
|
are parameterized for metal :doc:`units <units>`.
|
|
You can use the SW potential with any LAMMPS units, but you would need
|
|
to create your own EDIP potential file with coefficients listed in the
|
|
appropriate units if your simulation doesn't use "metal" units.
|
|
|
|
Related commands
|
|
""""""""""""""""
|
|
|
|
:doc:`pair_coeff <pair_coeff>`
|
|
|
|
**Default:** none
|
|
|
|
|
|
----------
|
|
|
|
|
|
.. _EDIP:
|
|
|
|
|
|
|
|
**(EDIP)** J. F. Justo et al., Phys. Rev. B 58, 2539 (1998).
|
|
|
|
|
|
.. _lws: http://lammps.sandia.gov
|
|
.. _ld: Manual.html
|
|
.. _lc: Section_commands.html#comm
|