mirror of https://github.com/lammps/lammps.git
168 lines
5.3 KiB
Plaintext
168 lines
5.3 KiB
Plaintext
pair_style meam/spline
|
|
======================
|
|
|
|
pair_style meam/spline/omp
|
|
==========================
|
|
|
|
Syntax
|
|
""""""
|
|
|
|
.. parsed-literal::
|
|
|
|
pair_style meam/spline
|
|
|
|
Examples
|
|
""""""""
|
|
|
|
.. parsed-literal::
|
|
|
|
pair_style meam/spline
|
|
pair_coeff * * Ti.meam.spline Ti
|
|
pair_coeff * * Ti.meam.spline Ti Ti Ti
|
|
|
|
Description
|
|
"""""""""""
|
|
|
|
The *meam/spline* style computes pairwise interactions for metals
|
|
using a variant of modified embedded-atom method (MEAM) potentials
|
|
:ref:`(Lenosky) <Lenosky>`. The total energy E is given by
|
|
|
|
.. image:: Eqs/pair_meam_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 five functions Phi, 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.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
|
|
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 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/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 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.spline file has values for Ti. If
|
|
your LAMMPS simulation has 3 atoms types and they are all to be
|
|
treated with this potentials, you would use the following pair_coeff
|
|
command:
|
|
|
|
.. parsed-literal::
|
|
|
|
pair_coeff * * Ti.meam.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/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/spline* style currently supports only single-element
|
|
MEAM potentials. It may be extended for alloy systems in the future.
|
|
|
|
|
|
----------
|
|
|
|
|
|
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**\ :
|
|
|
|
The current version of this 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/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/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>`
|
|
|
|
**Default:** none
|
|
|
|
|
|
----------
|
|
|
|
|
|
.. _Lenosky:
|
|
|
|
|
|
|
|
**(Lenosky)** Lenosky, Sadigh, Alonso, Bulatov, de la Rubia, Kim, Voter,
|
|
Kress, Modelling Simulation Materials Science Enginerring, 8, 825
|
|
(2000).
|
|
|
|
|
|
.. _lws: http://lammps.sandia.gov
|
|
.. _ld: Manual.html
|
|
.. _lc: Section_commands.html#comm
|