forked from lijiext/lammps
165 lines
5.4 KiB
Plaintext
165 lines
5.4 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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pair_style atm command :h3
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[Syntax:]
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pair_style atm cutoff cutoff_triple :pre
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cutoff = cutoff for each pair in 3-body interaction (distance units)
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cutoff_triple = additional cutoff applied to product of 3 pairwise distances (distance units) :ul
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[Examples:]
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pair_style atm 4.5 2.5
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pair_coeff * * * 0.072 :pre
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pair_style hybrid/overlay lj/cut 6.5 atm 4.5 2.5
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pair_coeff * * lj/cut 1.0 1.0
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pair_coeff 1 1 atm 1 0.064
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pair_coeff 1 1 atm 2 0.080
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pair_coeff 1 2 atm 2 0.100
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pair_coeff 2 2 atm 2 0.125 :pre
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[Description:]
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The {atm} style computes a 3-body "Axilrod-Teller-Muto"_#Axilrod
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potential for the energy E of a system of atoms as
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:c,image(Eqs/pair_atm.jpg)
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where nu is the three-body interaction strength. The distances
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between pairs of atoms r12, r23, r31 and the angles gamma1, gamma2,
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gamma3 are as shown in this diagram:
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:c,image(JPG/pair_atm_dia.jpg)
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Note that for the interaction between a triplet of atoms I,J,K, there
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is no "central" atom. The interaction is symmetric with respect to
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permutation of the three atoms. Thus the nu value is
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the same for all those permutations of the atom types of I,J,K
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and needs to be specified only once, as discussed below.
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The {atm} potential is typically used in combination with a two-body
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potential using the "pair_style hybrid/overlay"_pair_hybrid.html
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command as in the example above.
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The potential for a triplet of atom is calculated only if all 3
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distances r12, r23, r31 between the 3 atoms satisfy rIJ < cutoff.
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In addition, the product of the 3 distances r12*r23*r31 <
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cutoff_triple^3 is required, which excludes from calculation the
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triplets with small contribution to the interaction.
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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 restart files read by the
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"read_restart"_read_restart.html commands:
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K = atom type of the third atom (1 to Ntypes)
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nu = prefactor (energy/distance^9 units) :ul
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K can be specified in one of two ways. An explicit numeric value can
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be used, as in the 2nd example above. J <= K is required. LAMMPS
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sets the coefficients for the other 5 symmetric interactions to the
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same values. E.g. if I = 1, J = 2, K = 3, then these 6 values are set
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to the specified nu: nu123, nu132, nu213, nu231, nu312, nu321. This
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enforces the symmetry discussed above.
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A wildcard asterisk can be used for K to set the coefficients for
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multiple triplets of atom types. This takes the form "*" or "*n" or
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"n*" or "m*n". If N = the number of atom types, then an asterisk with
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no numeric values means all types from 1 to N. A leading asterisk
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means all types from 1 to n (inclusive). A trailing asterisk means
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all types from n to N (inclusive). A middle asterisk means all types
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from m to n (inclusive). Note that only type triplets with J <= K are
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considered; if asterisks imply type triplets where K < J, they are
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ignored.
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Note that a pair_coeff command can override a previous setting for the
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same I,J,K triplet. For example, these commands set nu for all I,J.K
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triplets, then overwrite nu for just the I,J,K = 2,3,4 triplet:
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pair_coeff * * * 0.25
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pair_coeff 2 3 4 0.1 :pre
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Note that for a simulation with a single atom type, only a single
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entry is required, e.g.
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pair_coeff 1 1 1 0.25 :pre
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For a simulation with two atom types, four pair_coeff commands will
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specify all possible nu values:
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pair_coeff 1 1 1 nu1
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pair_coeff 1 1 2 nu2
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pair_coeff 1 2 2 nu3
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pair_coeff 2 2 2 nu4 :pre
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For a simulation with three atom types, ten pair_coeff commands will
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specify all possible nu values:
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pair_coeff 1 1 1 nu1
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pair_coeff 1 1 2 nu2
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pair_coeff 1 1 3 nu3
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pair_coeff 1 2 2 nu4
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pair_coeff 1 2 3 nu5
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pair_coeff 1 3 3 nu6
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pair_coeff 2 2 2 nu7
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pair_coeff 2 2 3 nu8
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pair_coeff 2 3 3 nu9
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pair_coeff 3 3 3 nu10 :pre
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By default the nu value for all triplets is set to 0.0. Thus it is
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not required to provide pair_coeff commands that enumerate triplet
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interactions for all K types. If some I,J,K combination is not
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specified, then there will be no 3-body ATM interactions for that
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combination and all its permutations. However, as with all pair
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styles, it is required to specify a pair_coeff command for all I,J
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combinations, else an error will result.
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:line
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[Mixing, shift, table, tail correction, restart, rRESPA info]:
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This pair styles do not support the "pair_modify"_pair_modify.html
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mix, shift, table, and tail options.
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This pair style writes 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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However, if the {atm} potential is used in combination with other
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potentials using the "pair_style hybrid/overlay"_pair_hybrid.html
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command then pair_coeff commands need to be re-specified
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in the restart input script.
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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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This pair style is part of the MANYBODY package. It is only enabled
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if 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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[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(Axilrod)
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[(Axilrod)]
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Axilrod and Teller, J Chem Phys, 11, 299 (1943);
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Muto, Nippon Sugaku-Buturigakkwaishi 17, 629 (1943).
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