forked from lijiext/lammps
98 lines
3.6 KiB
Plaintext
98 lines
3.6 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,Section_commands.html#comm)
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:line
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fix qeq/reax command :h3
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[Syntax:]
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fix ID group-ID qeq/reax Nevery cutlo cuthi tolerance params :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 :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, 1991)"_#Rappe_1991 and formulated in "(Nakano,
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1997)"_#Nakano_1997. It is typically used in conjunction with the
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ReaxFF force field model as implemented in the "pair_style
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reax/c"_pair_reax_c.html command, but it can be used with any
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potential in LAMMPS, so long as it defines and uses charges on each
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atom. The "fix qeq/comb"_fix_qeq_comb.html command should be used to
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perform charge equliibration with the "COMB potential"_pair_comb.html.
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For more technical details about the charge equilibration performed by
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fix qeq/reax, see the "(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 reqires 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_reax_c.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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[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"_Section_howto.html#howto_15. No parameter of this fix can
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be used 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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[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 "Making
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LAMMPS"_Section_start.html#start_3 section 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_reax_c.html
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[Default:] none
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:line
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:link(Rappe_1991)
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[(Rappe)] Rappe and Goddard III, Journal of Physical Chemistry, 105,
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3358-3363 (1991).
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:link(Nakano_1997)
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[(Nakano)] Nakano, Computer Physics Communications, 104, 59-69 (1997).
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:link(Aktulga) [(Aktulga)] Aktulga, Fogarty, Pandit, Grama, Parallel
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Computing, to appear (2011).
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