forked from lijiext/lammps
257 lines
9.3 KiB
Plaintext
257 lines
9.3 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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pair_style coul/cut command :h3
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pair_style coul/cut/gpu command :h3
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pair_style coul/cut/omp command :h3
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pair_style coul/debye command :h3
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pair_style coul/debye/gpu command :h3
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pair_style coul/debye/omp command :h3
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pair_style coul/dsf command :h3
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pair_style coul/dsf/gpu command :h3
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pair_style coul/dsf/omp command :h3
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pair_style coul/long command :h3
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pair_style coul/long/omp command :h3
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pair_style coul/long/gpu command :h3
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pair_style coul/msm command :h3
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pair_style coul/msm/omp command :h3
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pair_style coul/wolf command :h3
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pair_style coul/wolf/omp command :h3
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pair_style tip4p/cut command :h3
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pair_style tip4p/long command :h3
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pair_style tip4p/cut/omp command :h3
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pair_style tip4p/long/omp command :h3
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[Syntax:]
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pair_style coul/cut cutoff
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pair_style coul/debye kappa cutoff
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pair_style coul/dsf alpha cutoff
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pair_style coul/long cutoff
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pair_style coul/long/gpu cutoff
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pair_style coul/wolf alpha cutoff
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pair_style tip4p/cut otype htype btype atype qdist cutoff
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pair_style tip4p/long otype htype btype atype qdist cutoff :pre
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cutoff = global cutoff for Coulombic interactions
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kappa = Debye length (inverse distance units)
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alpha = damping parameter (inverse distance units) :ul
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[Examples:]
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pair_style coul/cut 2.5
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pair_coeff * *
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pair_coeff 2 2 3.5 :pre
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pair_style coul/debye 1.4 3.0
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pair_coeff * *
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pair_coeff 2 2 3.5 :pre
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pair_style coul/dsf 0.05 10.0
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pair_coeff * * :pre
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pair_style coul/long 10.0
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pair_coeff * * :pre
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pair_style coul/msm 10.0
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pair_coeff * * :pre
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pair_style coul/wolf 0.2 9.0
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pair_coeff * * :pre
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pair_style tip4p/cut 1 2 7 8 0.15 12.0
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pair_coeff * * :pre
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pair_style tip4p/long 1 2 7 8 0.15 10.0
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pair_coeff * * :pre
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[Description:]
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The {coul/cut} style computes the standard Coulombic interaction
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potential given by
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:c,image(Eqs/pair_coulomb.jpg)
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where C is an energy-conversion constant, Qi and Qj are the charges on
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the 2 atoms, and epsilon is the dielectric constant which can be set
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by the "dielectric"_dielectric.html command. The cutoff Rc truncates
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the interaction distance.
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Style {coul/debye} adds an additional exp() damping factor to the
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Coulombic term, given by
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:c,image(Eqs/pair_debye.jpg)
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where kappa is the Debye length. This potential is another way to
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mimic the screening effect of a polar solvent.
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Style {coul/dsf} computes Coulombic interactions via the damped
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shifted force model described in "Fennell"_#Fennell, given by:
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:c,image(Eqs/pair_coul_dsf.jpg)
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where {alpha} is the damping parameter and erfc() is the
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complementary error-function. The potential corrects issues in the
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Wolf model (described below) to provide consistent forces and energies
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(the Wolf potential is not differentiable at the cutoff) and smooth
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decay to zero.
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Style {coul/wolf} computes Coulombic interactions via the Wolf
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summation method, described in "Wolf"_#Wolf, given by:
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:c,image(Eqs/pair_coul_wolf.jpg)
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where {alpha} is the damping parameter, and erc() and erfc() are
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error-fuction and complementary error-function terms. This potential
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is essentially a short-range, spherically-truncated,
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charge-neutralized, shifted, pairwise {1/r} summation. With a
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manipulation of adding and substracting a self term (for i = j) to the
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first and second term on the right-hand-side, respectively, and a
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small enough {alpha} damping parameter, the second term shrinks and
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the potential becomes a rapidly-converging real-space summation. With
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a long enough cutoff and small enough alpha parameter, the energy and
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forces calcluated by the Wolf summation method approach those of the
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Ewald sum. So it is a means of getting effective long-range
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interactions with a short-range potential.
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Styles {coul/long} and {coul/msm} compute the same Coulombic
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interactions as style {coul/cut} except that an additional damping
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factor is applied so it can be used in conjunction with the
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"kspace_style"_kspace_style.html command and its {ewald} or {pppm}
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option. The Coulombic cutoff specified for this style means that
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pairwise interactions within this distance are computed directly;
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interactions outside that distance are computed in reciprocal space.
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Styles {tip4p/cut} and {tip4p/long} implement the coulomb part of
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the TIP4P water model of "(Jorgensen)"_#Jorgensen, which introduces
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a massless site located a short distance away from the oxygen atom
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along the bisector of the HOH angle. The atomic types of the oxygen and
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hydrogen atoms, the bond and angle types for OH and HOH interactions,
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and the distance to the massless charge site are specified as
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pair_style arguments. Style {tip4p/cut} uses a global cutoff for
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Coulomb interactions; style {tip4p/long} is for use with a long-range
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Coulombic solver (Ewald or PPPM).
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IMPORTANT NOTE: For each TIP4P water molecule in your system, the atom
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IDs for the O and 2 H atoms must be consecutive, with the O atom
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first. This is to enable LAMMPS to "find" the 2 H atoms associated
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with each O atom. For example, if the atom ID of an O atom in a TIP4P
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water molecule is 500, then its 2 H atoms must have IDs 501 and 502.
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See the "howto section"_Section_howto.html#howto_8 for more
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information on how to use the TIP4P pair styles and lists of
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parameters to set. Note that the neighobr list cutoff for Coulomb
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interactions is effectively extended by a distance 2*qdist when using
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the TIP4P pair style, to account for the offset distance of the
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fictitious charges on O atoms in water molecules. Thus it is
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typically best in an efficiency sense to use a LJ cutoff >= Coulomb
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cutoff + 2*qdist, to shrink the size of the neighbor list. This leads
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to slightly larger cost for the long-range calculation, so you can
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test the trade-off for your model.
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These potentials are designed to be combined with other pair
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potentials via the "pair_style hybrid/overlay"_pair_hybrid.html
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command. This is because they have no repulsive core. Hence if they
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are used by themselves, there will be no repulsion to keep two
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oppositely charged particles from overlapping each other.
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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, or by mixing as described below:
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cutoff (distance units) :ul
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For {coul/cut} and {coul/debye}, the cutoff coefficient is optional.
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If it is not used (as in some of the examples above), the default
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global value specified in the pair_style command is used.
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For {coul/long} and {coul/msm} no cutoff can be specified for an
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individual I,J type pair via the pair_coeff command. All type pairs
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use the same global Coulombic cutoff specified in the pair_style
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command.
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:line
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Styles with a {cuda}, {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 in "Section_accelerate"_Section_accelerate.html
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of the manual. The accelerated styles take the same arguments and
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should produce the same results, except for round-off and precision
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issues.
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These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
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KOKKOS, USER-OMP and OPT packages, respectively. They are only
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enabled if LAMMPS was built with those packages. See the "Making
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LAMMPS"_Section_start.html#start_3 section 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"_Section_start.html#start_7 when you invoke LAMMPS, or you can
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use the "suffix"_suffix.html command in your input script.
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See "Section_accelerate"_Section_accelerate.html of the manual for
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more instructions on how to use the accelerated styles effectively.
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:line
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[Mixing, shift, table, tail correction, restart, rRESPA info]:
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For atom type pairs I,J and I != J, the cutoff distance for the
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{coul/cut} style can be mixed. The default mix value is {geometric}.
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See the "pair_modify" command for details.
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The "pair_modify"_pair_modify.html shift option is not relevant
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for these pair styles.
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The {coul/long} style supports the "pair_modify"_pair_modify.html
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table option for tabulation of the short-range portion of the
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long-range Coulombic interaction.
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These pair styles do not support the "pair_modify"_pair_modify.html
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tail option for adding long-range tail corrections to energy and
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pressure.
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These pair styles write their 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 can only be used via the {pair} keyword of the
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"run_style respa"_run_style.html command. It does not support the
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{inner}, {middle}, {outer} keywords.
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:line
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[Restrictions:]
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The {coul/long}, {coul/msm} and {tip4p/long} styles are part of the
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KSPACE package. They are only enabled if LAMMPS was built with that
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package (which it is by default).
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See the "Making LAMMPS"_Section_start.html#start_3 section
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for more info.
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[Related commands:]
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"pair_coeff"_pair_coeff.html, "pair_style
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hybrid/overlay"_pair_hybrid.html
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"kspace_style"_kspace_style.html
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[Default:] none
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:line
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:link(Wolf)
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[(Wolf)] D. Wolf, P. Keblinski, S. R. Phillpot, J. Eggebrecht, J Chem
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Phys, 110, 8254 (1999).
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:link(Fennell)
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[(Fennell)] C. J. Fennell, J. D. Gezelter, J Chem Phys, 124,
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234104 (2006).
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