forked from lijiext/lammps
150 lines
5.5 KiB
Plaintext
150 lines
5.5 KiB
Plaintext
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"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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pair_style buck/coul command :h3
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[Syntax:]
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pair_style buck/coul flag_buck flag_coul cutoff (cutoff2) :pre
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flag_buck = {long} or {cut} :ulb,l
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{long} = use Kspace long-range summation for the dispersion term 1/r^6
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{cut} = use a cutoff :pre
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flag_coul = {long} or {off} :l
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{long} = use Kspace long-range summation for the Coulombic term 1/r
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{off} = omit the Coulombic term :pre
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cutoff = global cutoff for Buckingnham (and Coulombic if only 1 cutoff) (distance units) :l
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cutoff2 = global cutoff for Coulombic (optional) (distance units) :l,ule
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[Examples:]
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pair_style buck/coul cut off 2.5
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pair_style buck/coul cut long 2.5 4.0
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pair_style buck/coul long long 2.5 4.0
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pair_coeff * * 1 1
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pair_coeff 1 1 1 3 4 :pre
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[Description:]
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The {buck/coul} style computes a Buckingham potential (exp/6 instead of
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Lennard-Jones 12/6) and Coulombic potential, given by
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:c,image(Eqs/pair_buck.jpg)
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:c,image(Eqs/pair_coulomb.jpg)
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Rc is the cutoff. If one cutoff is specified in the pair_style
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command, it is used for both the Buckingham and Coulombic terms. If
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two cutoffs are specified, they are used as cutoffs for the Buckingham
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and Coulombic terms respectively.
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The purpose of this pair style is to capture long-range interactions
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resulting from both attractive 1/r^6 Buckingham and Coulombic 1/r
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interactions. This is done by use of the {flag_lj} and {flag_coul}
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settings. The ""Ismail"_#Ismail paper has more details on when it is
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appropriate to include long-range 1/r^6 interactions, using this
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potential.
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If {flag_lj} is set to {long}, no cutoff is used on the Buckingham
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1/r^6 dispersion term. The long-range portion is calculated by using
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the "kspace_style ewald/n"_kspace_style.html command. The specified
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Buckingham cutoff then determines which portion of the Buckingham
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interactions are computed directly by the pair potential versus which
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part is computed in reciprocal space via the Kspace style. If
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{flag_lj} is set to {cut}, the Buckingham interactions are simply
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cutoff, as with "pair_style buck"_pair_buck.html.
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If {flag_coul} is set to {long}, no cutoff is used on the Coulombic
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interactions. The long-range portion is calculated by using any
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style, including {ewald/n} of the "kspace_style"_kspace_style.html
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command. Note that if {flag_buck} is also set to long, then only the
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{ewald/n} Kspace style can perform the long-range calculations for
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both the Buckingham and Coulombic interactions. If {flag_coul} is set
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to {off}, Coulombic interactions are not computed.
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The following coefficients must be defined for each pair of atoms
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types via the "pair_coeff"_pair_coeff.html command as in the examples
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above, or in the data file or restart files read by the
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"read_data"_read_data.html or "read_restart"_read_restart.html
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commands:
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A (energy units)
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rho (distance units)
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C (energy-distance^6 units)
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cutoff (distance units)
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cutoff2 (distance units) :ul
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The second coefficient, rho, must be greater than zero.
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The latter 2 coefficients are optional. If not specified, the global
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Buckingham and Coulombic cutoffs specified in the pair_style command
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are used. If only one cutoff is specified, it is used as the cutoff
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for both Buckingham and Coulombic interactions for this type pair. If
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both coefficients are specified, they are used as the Buckingham and
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Coulombic cutoffs for this type pair. Note that if you are using
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{flag_buck} set to {long}, you cannot specify a Buckingham cutoff for
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an atom type pair, since only one global Buckingham cutoff is allowed.
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Similarly, if you are using {flag_coul} set to {long}, you cannot
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specify a Coulombic cutoff for an atom type pair, since only one
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global Coulombic cutoff is allowed.
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:line
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[Mixing, shift, table, tail correction, per-atom energy/stress,
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restart, and rRESPA info]:
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This pair styles does not support mixing. Thus, coefficients for all
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I,J pairs must be specified explicitly.
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This pair style supports the "pair_modify"_pair_modify.html shift
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option for the energy of the exp() and 1/r^6 portion of the pair
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interaction, assuming {flag_buck} is {cut}.
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This pair style does not support the "pair_modify"_pair_modify.html
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shift option for the energy of the Buckingham portion of the pair
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interaction.
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This pair style does not support the "pair_modify"_pair_modify.html
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table option since a tabulation capability has not yet been added to
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this potential.
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This pair style can calculate per-atom energy and stress, as used by
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the "compute epair/atom"_compute_epair_atom.html, "compute
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stress/atom"_compute_stress_atom.html, and "dump custom"_dump.html
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commands.
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This pair style write its information to "binary restart
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files"_restart.html, so pair_style and pair_coeff commands do not need
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to be specified in an input script that reads a restart file.
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This pair style supports the use of the {inner}, {middle}, and {outer}
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keywords of the "run_style respa"_run_style.html command, meaning the
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pairwise forces can be partitioned by distance at different levels of
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the rRESPA hierarchy. See the "run_style"_run_style.html command for
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details.
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:line
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[Restrictions:]
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This style is part of the "user-ewaldn" package. It is only enabled
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if LAMMPS was built with that package. See the "Making
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LAMMPS"_Section_start.html#2_3 section for more info.
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[Related commands:]
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"pair_coeff"_pair_coeff.html
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[Default:] none
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:line
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:link(Ismail)
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[(Ismail)] Ismail, Tsige, In 't Veld, Grest, Molecular Physics
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(accepted) (2007).
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