forked from lijiext/lammps
100 lines
3.3 KiB
Plaintext
100 lines
3.3 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/comb command :h3
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[Syntax:]
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fix ID group-ID qeq/comb Nevery precision keyword value ... :pre
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ID, group-ID are documented in "fix"_fix.html command :ulb,l
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qeq/comb = style name of this fix command :l
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Nevery = perform charge equilibration every this many steps :l
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precision = convergence criterion for charge equilibration :l
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zero or more keyword/value pairs may be appended :l
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keyword = {file} :l
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{file} value = filename
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filename = name of file to write QEQ equilibration info to :pre
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:ule
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[Examples:]
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fix 1 surface qeq/comb 10 0.0001 :pre
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[Description:]
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This fix is designed for use with the pair_style comb command which
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implements the COMB COMB (Charge-Optimized Many-Body) potential as
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described in "(COMB_1)"_#COMB_1 and "(COMB_2)"_#COMB_2. It performs
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the charge equilibration portion of the calculation using the
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so-called QEq method, whereby the charge on each atom is adjusted to
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minimize the energy of the system.
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Only charges on the atoms in the specified group are equilibrated.
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The fix relies on the pair style (COMB in this case) to calculate the
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per-atom electronegativity (effective force on the charges). An
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electronegativity equalization calculation (or QEq) is performed in an
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interative fashion, which in parallel requires communication at each
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iteration for processors to exchange charge information about nearby
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atoms with each other. See "Rappe_and_Goddard"_#Rappe_and_Goddard and
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"Rick_and_Stuart"_#Rick_and_Stuart for details.
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During a run, charge equilibration is peformed every {Nevery} time
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steps. Charge equilibration is also always enforced on the first step
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of each run. The {precision} argument controls the tolerance for the
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difference in electronegativity for all atoms during charge
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equilibration. {Precision} is a trade-off between the cost of
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performing charge equilibration (more iterations) and accuracy.
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If the {file} keyword is used, then information about each
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equilibration calculation is written to the specifed file.
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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. None of the "fix_modify"_fix_modify.html options
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are relevant to this fix.
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This fix produces a per-atom vector which can be accessed by various
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"output commands"_Section_howto.html#4_15. The vector stores the
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gradient of the charge on each atom. The per-atom values be accessed
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on any timestep.
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No parameter of this fix can be used with the {start/stop} keywords of
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the "run"_run.html command. This fix is not invoked during "energy
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minimization"_minimize.html.
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[Restrictions:]
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This fix command currently only supports "pair style {comb}"_pair_comb.html.
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[Related commands:]
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"pair_style comb"_pair_comb.html
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[Default:]
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No file output is performed.
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:line
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:link(COMB_1)
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[(COMB_1)] J. Yu, S. B. Sinnott, S. R. Phillpot, Phys Rev B, 75, 085311 (2007),
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:link(COMB_2)
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[(COMB_2)] T.-R. Shan, B. D. Devine, T. W. Kemper, S. B. Sinnott, S. R.
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Phillpot, Phys Rev B, 81, 125328 (2010).
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:link(Rappe_and_Goddard)
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[(Rappe_and_Goddard)] A. K. Rappe, W. A. Goddard, J Phys Chem 95, 3358
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(1991).
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:link(Rick_and_Stuart)
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[(Rick_and_Stuart)] S. W. Rick, S. J. Stuart, B. J. Berne, J Chem Phys
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101, 16141 (1994).
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