forked from lijiext/lammps
130 lines
4.8 KiB
Plaintext
130 lines
4.8 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Commands_all.html)
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:line
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fix qeq/reax command :h3
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fix qeq/reax/kk command :h3
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fix qeq/reax/omp command :h3
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[Syntax:]
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fix ID group-ID qeq/reax Nevery cutlo cuthi tolerance params args :pre
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ID, group-ID are documented in "fix"_fix.html command
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qeq/reax = style name of this fix command
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Nevery = perform QEq every this many steps
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cutlo,cuthi = lo and hi cutoff for Taper radius
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tolerance = precision to which charges will be equilibrated
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params = reax/c or a filename
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args = {dual} (optional) :ul
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[Examples:]
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fix 1 all qeq/reax 1 0.0 10.0 1.0e-6 reax/c
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fix 1 all qeq/reax 1 0.0 10.0 1.0e-6 param.qeq :pre
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[Description:]
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Perform the charge equilibration (QEq) method as described in "(Rappe
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and Goddard)"_#Rappe2 and formulated in "(Nakano)"_#Nakano2. It is
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typically used in conjunction with the ReaxFF force field model as
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implemented in the "pair_style reax/c"_pair_reaxc.html command, but
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it can be used with any potential in LAMMPS, so long as it defines and
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uses charges on each atom. The "fix qeq/comb"_fix_qeq_comb.html
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command should be used to perform charge equilibration with the "COMB
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potential"_pair_comb.html. For more technical details about the
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charge equilibration performed by fix qeq/reax, see the
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"(Aktulga)"_#qeq-Aktulga paper.
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The QEq method minimizes the electrostatic energy of the system by
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adjusting the partial charge on individual atoms based on interactions
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with their neighbors. It requires some parameters for each atom type.
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If the {params} setting above is the word "reax/c", then these are
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extracted from the "pair_style reax/c"_pair_reaxc.html command and
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the ReaxFF force field file it reads in. If a file name is specified
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for {params}, then the parameters are taken from the specified file
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and the file must contain one line for each atom type. The latter
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form must be used when performing QeQ with a non-ReaxFF potential.
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Each line should be formatted as follows:
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itype chi eta gamma :pre
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where {itype} is the atom type from 1 to Ntypes, {chi} denotes the
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electronegativity in eV, {eta} denotes the self-Coulomb
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potential in eV, and {gamma} denotes the valence orbital
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exponent. Note that these 3 quantities are also in the ReaxFF
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potential file, except that eta is defined here as twice the eta value
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in the ReaxFF file. Note that unlike the rest of LAMMPS, the units
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of this fix are hard-coded to be A, eV, and electronic charge.
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The optional {dual} keyword allows to perform the optimization
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of the S and T matrices in parallel. This is only supported for
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the {qeq/reax/omp} style. Otherwise they are processed separately.
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[Restart, fix_modify, output, run start/stop, minimize info:]
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No information about this fix is written to "binary restart
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files"_restart.html. No global scalar or vector or per-atom
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quantities are stored by this fix for access by various "output
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commands"_Howto_output.html. No parameter of this fix can be used
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with the {start/stop} keywords of the "run"_run.html command.
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This fix is invoked during "energy minimization"_minimize.html.
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:line
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Styles with a {gpu}, {intel}, {kk}, {omp}, or {opt} suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed on the "Speed packages"_Speed_packages.html doc
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page. The accelerated styles take the same arguments and should
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produce the same results, except for round-off and precision issues.
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These accelerated styles are part of the GPU, USER-INTEL, KOKKOS,
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USER-OMP and OPT packages, respectively. They are only enabled if
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LAMMPS was built with those packages. See the "Build
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package"_Build_package.html doc page for more info.
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You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the "-suffix command-line
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switch"_Run_options.html when you invoke LAMMPS, or you can use the
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"suffix"_suffix.html command in your input script.
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See the "Speed packages"_Speed_packages.html doc page for more
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instructions on how to use the accelerated styles effectively.
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:line
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[Restrictions:]
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This fix is part of the USER-REAXC package. It is only enabled if
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LAMMPS was built with that package. See the "Build
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package"_Build_package.html doc page for more info.
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This fix does not correctly handle interactions
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involving multiple periodic images of the same atom. Hence, it should not
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be used for periodic cell dimensions less than 10 angstroms.
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[Related commands:]
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"pair_style reax/c"_pair_reaxc.html
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[Default:] none
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:line
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:link(Rappe2)
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[(Rappe)] Rappe and Goddard III, Journal of Physical Chemistry, 95,
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3358-3363 (1991).
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:link(Nakano2)
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[(Nakano)] Nakano, Computer Physics Communications, 104, 59-69 (1997).
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:link(qeq-Aktulga)
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[(Aktulga)] Aktulga, Fogarty, Pandit, Grama, Parallel Computing, 38,
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245-259 (2012).
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