Homec4science
Diffusion lammps (master) Browse

lammps/doc/src/pair_adp.txt
2f298951cff2master

Last Change
Raw File

pair_adp.txt
View Options

"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)
:line
pair_style adp command :h3
pair_style adp/omp command :h3
[Syntax:]
pair_style adp :pre
[Examples:]
pair_style adp
pair_coeff * * Ta.adp Ta
pair_coeff * * ../potentials/AlCu.adp Al Al Cu :pre
[Description:]
Style {adp} computes pairwise interactions for metals and metal alloys
using the angular dependent potential (ADP) of "(Mishin)"_#Mishin,
which is a generalization of the "embedded atom method (EAM)
potential"_pair_eam.html. The LAMMPS implementation is discussed in
"(Singh)"_#Singh. The total energy Ei of an atom I is given by
:c,image(Eqs/pair_adp.jpg)
where F is the embedding energy which is a function of the atomic
electron density rho, phi is a pair potential interaction, alpha and
beta are the element types of atoms I and J, and s and t = 1,2,3 and
refer to the cartesian coordinates. The mu and lambda terms represent
the dipole and quadruple distortions of the local atomic environment
which extend the original EAM framework by introducing angular forces.
Note that unlike for other potentials, cutoffs for ADP potentials are
not set in the pair_style or pair_coeff command; they are specified in
the ADP potential files themselves. Likewise, the ADP potential files
list atomic masses; thus you do not need to use the "mass"_mass.html
command to specify them.
The NIST WWW site distributes and documents ADP potentials:
http://www.ctcms.nist.gov/potentials :pre
Note that these must be converted into the extended DYNAMO {setfl}
format discussed below.
The NIST site is maintained by Chandler Becker (cbecker at nist.gov)
who is good resource for info on interatomic potentials and file
formats.
:line
Only a single pair_coeff command is used with the {adp} style which
specifies an extended DYNAMO {setfl} file, which contains information
for M 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 extended {setfl} elements to atom types :ul
See the "pair_coeff"_pair_coeff.html doc page for alternate ways to
specify the path for the potential file.
As an example, the potentials/AlCu.adp file, included in the
potentials directory of the LAMMPS distrbution, is an extended {setfl}
file which has tabulated ADP values for w elements and their alloy
interactions: Cu and Al. If your LAMMPS simulation has 4 atoms types
and you want the 1st 3 to be Al, and the 4th to be Cu, you would use
the following pair_coeff command:
pair_coeff * * AlCu.adp Al Al Al Cu :pre
The 1st 2 arguments must be * * so as to span all LAMMPS atom types.
The first three Al arguments map LAMMPS atom types 1,2,3 to the Al
element in the extended {setfl} file. The final Cu argument maps
LAMMPS atom type 4 to the Al element in the extended {setfl} file.
Note that there is no requirement that your simulation use all the
elements specified by the extended {setfl} file.
If a mapping value is specified as NULL, the mapping is not performed.
This can be used when an {adp} 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.
{Adp} files in the {potentials} directory of the LAMMPS distribution
have an ".adp" suffix. A DYNAMO {setfl} file extended for ADP is
formatted as follows. Basically it is the standard {setfl} format
with additional tabulated functions u and w added to the file after
the tabulated pair potentials. See the "pair_eam"_pair_eam.html
command for further details on the {setfl} format.
lines 1,2,3 = comments (ignored)
line 4: Nelements Element1 Element2 ... ElementN
line 5: Nrho, drho, Nr, dr, cutoff :ul
Following the 5 header lines are Nelements sections, one for each
element, each with the following format:
line 1 = atomic number, mass, lattice constant, lattice type (e.g. FCC)
embedding function F(rho) (Nrho values)
density function rho(r) (Nr values) :ul
Following the Nelements sections, Nr values for each pair potential
phi(r) array are listed for all i,j element pairs in the same format
as other arrays. Since these interactions are symmetric (i,j = j,i)
only phi arrays with i >= j are listed, in the following order: i,j =
(1,1), (2,1), (2,2), (3,1), (3,2), (3,3), (4,1), ..., (Nelements,
Nelements). The tabulated values for each phi function are listed as
r*phi (in units of eV-Angstroms), since they are for atom pairs, the
same as for "other EAM files"_pair_eam.html.
After the phi(r) arrays, each of the u(r) arrays are listed in the
same order with the same assumptions of symmetry. Directly following
the u(r), the w(r) arrays are listed. Note that phi(r) is the only
array tabulated with a scaling by r.
:line
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 "Section 5"_Section_accelerate.html
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 "Making
LAMMPS"_Section_start.html#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 "-suffix command-line
switch"_Section_start.html#start_7 when you invoke LAMMPS, or you can
use the "suffix"_suffix.html command in your input script.
See "Section 5"_Section_accelerate.html of the manual for
more instructions on how to use the accelerated styles effectively.
:line
[Mixing, shift, table, tail correction, restart, rRESPA info]:
For atom type pairs I,J and I != J, where types I and J correspond to
two different element types, no special mixing rules are needed, since
the ADP potential files specify alloy interactions explicitly.
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 tabulated 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:]
This pair style is part of the MANYBODY package. It is only enabled
if LAMMPS was built with that package (which it is by default).
[Related commands:]
"pair_coeff"_pair_coeff.html, "pair_eam"_pair_eam.html
[Default:] none
:line
:link(Mishin)
[(Mishin)] Mishin, Mehl, and Papaconstantopoulos, Acta Mater, 53, 4029
(2005).
:link(Singh)
[(Singh)] Singh and Warner, Acta Mater, 58, 5797-5805 (2010),
c4science · Help