forked from lijiext/lammps
133 lines
4.9 KiB
Plaintext
133 lines
4.9 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
|
|
|
|
:link(lws,http://lammps.sandia.gov)
|
|
:link(ld,Manual.html)
|
|
:link(lc,Commands_all.html)
|
|
|
|
:line
|
|
|
|
pair_style agni command :h3
|
|
pair_style agni/omp command :h3
|
|
|
|
[Syntax:]
|
|
|
|
pair_style agni :pre
|
|
|
|
[Examples:]
|
|
pair_style agni
|
|
pair_coeff * * Al.agni Al
|
|
|
|
[Description:]
|
|
|
|
Style {agni} style computes the many-body vectorial force components for
|
|
an atom as
|
|
|
|
:c,image(Eqs/pair_agni.jpg)
|
|
|
|
{u} labels the individual components, i.e. x, y or z, and {V} is the
|
|
corresponding atomic fingerprint. {d} is the Euclidean distance between
|
|
any two atomic fingerprints. A total of N_t reference atomic
|
|
environments are considered to construct the force field file. {alpha_t}
|
|
and {l} are the weight coefficients and length scale parameter of the
|
|
non-linear regression model.
|
|
|
|
The method implements the recently proposed machine learning access to
|
|
atomic forces as discussed extensively in the following publications -
|
|
"(Botu1)"_#Botu2015adaptive and "(Botu2)"_#Botu2015learning. The premise
|
|
of the method is to map the atomic environment numerically into a
|
|
fingerprint, and use machine learning methods to create a mapping to the
|
|
vectorial atomic forces.
|
|
|
|
Only a single pair_coeff command is used with the {agni} style which
|
|
specifies an AGNI potential file containing the parameters of the
|
|
force field for the 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 AGNI elements to atom types :ul
|
|
|
|
See the "pair_coeff"_pair_coeff.html doc page for alternate ways
|
|
to specify the path for the force field file.
|
|
|
|
An AGNI force field is fully specified by the filename which contains the
|
|
parameters of the force field, i.e., the reference training environments
|
|
used to construct the machine learning force field. Example force field
|
|
and input files are provided in the examples/USER/misc/agni directory.
|
|
|
|
:line
|
|
|
|
Styles with {omp} suffix is functionally the same as the corresponding
|
|
style without the suffix. They have been optimized to run faster,
|
|
depending on your available hardware, as discussed on the "Speed
|
|
packages"_Speed_packages.html doc page. The accelerated style takes
|
|
the same arguments and should produce the same results, except for
|
|
round-off and precision issues.
|
|
|
|
The accelerated style is part of the USER-OMP. They are only enabled
|
|
if LAMMPS was built with those packages. See the "Build
|
|
package"_Build_package.html doc page for more info.
|
|
|
|
You can specify the accelerated style explicitly in your input script
|
|
by including their suffix, or you can use the "-suffix command-line
|
|
switch"_Run_options.html when you invoke LAMMPS, or you can use the
|
|
"suffix"_suffix.html command in your input script.
|
|
|
|
See the "Speed packages"_Speed_packages.html doc page for more
|
|
instructions on how to use the accelerated styles effectively.
|
|
|
|
:line
|
|
|
|
[Mixing, shift, table, tail correction, restart, rRESPA info]:
|
|
|
|
This pair style does not support the "pair_modify"_pair_modify.html
|
|
shift, table, and tail options.
|
|
|
|
This pair style does not write its information to "binary restart
|
|
files"_restart.html, 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
|
|
"run_style respa"_run_style.html command. It does not support the
|
|
{inner}, {middle}, {outer} keywords.
|
|
|
|
:line
|
|
|
|
[Restrictions:]
|
|
|
|
Currently, only elemental systems are implemented. Also, the method
|
|
only provides access to the forces and not energies or stresses.
|
|
The lack of potential energy data makes this pair style incompatible with
|
|
several of the "minimizer algorthms"_min_style.html like {cg} or {sd}.
|
|
It should work with damped dynamics based minimizers like {fire} or
|
|
{quickmin}. However, one can access the energy via thermodynamic
|
|
integration of the forces as discussed in
|
|
"(Botu3)"_#Botu2016construct. This pair style is part of the
|
|
USER-MISC package. It is only enabled if LAMMPS was built with that
|
|
package. See the "Build package"_Build_package.html doc page for more
|
|
info.
|
|
|
|
The AGNI force field files provided with LAMMPS (see the
|
|
potentials directory) are parameterized for metal "units"_units.html.
|
|
You can use the AGNI potential with any LAMMPS units, but you would need
|
|
to create your own AGNI potential file with coefficients listed in the
|
|
appropriate units if your simulation doesn't use "metal" units.
|
|
|
|
[Related commands:]
|
|
|
|
"pair_coeff"_pair_coeff.html
|
|
|
|
[Default:] none
|
|
|
|
:line
|
|
|
|
:link(Botu2015adaptive)
|
|
[(Botu1)] V. Botu and R. Ramprasad, Int. J. Quant. Chem., 115(16), 1074 (2015).
|
|
|
|
:link(Botu2015learning)
|
|
[(Botu2)] V. Botu and R. Ramprasad, Phys. Rev. B, 92(9), 094306 (2015).
|
|
|
|
:link(Botu2016construct)
|
|
[(Botu3)] V. Botu, R. Batra, J. Chapman and R. Ramprasad, https://arxiv.org/abs/1610.02098 (2016).
|