Description:
Set weighting coefficients for pairwise energy and force contributions -from atom pairs that are permanently bonded to each other. These -weighting factors are used by all pair styles in -LAMMPS that compute simple pairwise interactions. The Coulomb factors -are applied to any Coulomb (charge interaction) term that the -potential calculates. The LJ factors are applied to the remaining -terms that the potential calculates, whether they represent LJ -interactions or not. The weighting factors are a scaling pre-factor -on the energy and force between the pair of atoms. Permanent bonds -between atoms are specified by defining the bond topology in the data -file read by the read_data command and by using the -bond_style command to define the bond potential. +between pairs of atoms that are also permanently bonded to each other, +either directly or via one or two intermediate bonds. These weighting +factors are used by nearly all pair styles in LAMMPS +that compute simple pairwise interactions. Permanent bonds between +atoms are specified by defining the bond topology in the data file +read by the read_data command. Typically a +bond_style command is also used to define a bond +potential. The rationale for using these weighting factors is that +the interaction between a pair of bonded atoms is all (or mostly) +specified by the bond, angle, dihedral potentials, and thus the +non-bonded Lennard-Jones or Coulombic interaction between the pair of +atoms should be excluded (or reduced by a weighting factor).
IMPORTANT NOTE: These weighting factors are NOT used by pair styles that compute many-body interactions, since the "bonds" that result from such interactions are not permanent, but are created and broken dynamically as atom conformations change. Examples -of pair styles and potentials in this category are EAM, MEAM, -Stillinger-Weber, Tersoff, COMB, AIREBO, and ReaxFF. In fact, when -using these pair styles, it makes no sense to define permanent bonds -and to specify special_bonds weighting factors (unless they are -applied to a different part of the system via the pair_style -hybrid command). Though LAMMPS does not check for -this, using special_bonds with these potentials will result in errors -and possibly crash the code, because the definition of weighting -factors changes the format of the neighor list used by the pair -styles. +of pair styles in this category are EAM, MEAM, Stillinger-Weber, +Tersoff, COMB, AIREBO, and ReaxFF. In fact, it generally makes no +sense to define permanent bonds between atoms that interact via these +potentials, though such bonds may exist elsewhere in your system, +e.g. when using the pair_style hybrid command. +Thus LAMMPS ignores special_bonds settings when manybody potentials +are calculated. +
+The Coulomb factors are applied to any Coulomb (charge interaction) +term that the potential calculates. The LJ factors are applied to the +remaining terms that the potential calculates, whether they represent +LJ interactions or not. The weighting factors are a scaling +pre-factor on the energy and force between the pair of atoms. A value +of 1.0 means include the full interaction; a value of 0.0 means +exclude it completely.
The 1st of the 3 coefficients (LJ or Coulombic) is the weighting factor on 1-2 atom pairs, which are pairs of atoms directly bonded to diff --git a/doc/special_bonds.txt b/doc/special_bonds.txt index f5be9da5fb..758c68dca5 100644 --- a/doc/special_bonds.txt +++ b/doc/special_bonds.txt @@ -42,32 +42,38 @@ special_bonds lj/coul 0 1 1 extra 2 :pre [Description:] Set weighting coefficients for pairwise energy and force contributions -from atom pairs that are permanently bonded to each other. These -weighting factors are used by all "pair styles"_pair_style.html in -LAMMPS that compute simple pairwise interactions. The Coulomb factors -are applied to any Coulomb (charge interaction) term that the -potential calculates. The LJ factors are applied to the remaining -terms that the potential calculates, whether they represent LJ -interactions or not. The weighting factors are a scaling pre-factor -on the energy and force between the pair of atoms. Permanent bonds -between atoms are specified by defining the bond topology in the data -file read by the "read_data"_read_data.html command and by using the -"bond_style"_bond_style.html command to define the bond potential. +between pairs of atoms that are also permanently bonded to each other, +either directly or via one or two intermediate bonds. These weighting +factors are used by nearly all "pair styles"_pair_style.html in LAMMPS +that compute simple pairwise interactions. Permanent bonds between +atoms are specified by defining the bond topology in the data file +read by the "read_data"_read_data.html command. Typically a +"bond_style"_bond_style.html command is also used to define a bond +potential. The rationale for using these weighting factors is that +the interaction between a pair of bonded atoms is all (or mostly) +specified by the bond, angle, dihedral potentials, and thus the +non-bonded Lennard-Jones or Coulombic interaction between the pair of +atoms should be excluded (or reduced by a weighting factor). IMPORTANT NOTE: These weighting factors are NOT used by "pair styles"_pair_style.html that compute many-body interactions, since the "bonds" that result from such interactions are not permanent, but are created and broken dynamically as atom conformations change. Examples -of pair styles and potentials in this category are EAM, MEAM, -Stillinger-Weber, Tersoff, COMB, AIREBO, and ReaxFF. In fact, when -using these pair styles, it makes no sense to define permanent bonds -and to specify special_bonds weighting factors (unless they are -applied to a different part of the system via the "pair_style -hybrid"_pair_hybrid.html command). Though LAMMPS does not check for -this, using special_bonds with these potentials will result in errors -and possibly crash the code, because the definition of weighting -factors changes the format of the neighor list used by the pair -styles. +of pair styles in this category are EAM, MEAM, Stillinger-Weber, +Tersoff, COMB, AIREBO, and ReaxFF. In fact, it generally makes no +sense to define permanent bonds between atoms that interact via these +potentials, though such bonds may exist elsewhere in your system, +e.g. when using the "pair_style hybrid"_pair_hybrid.html command. +Thus LAMMPS ignores special_bonds settings when manybody potentials +are calculated. + +The Coulomb factors are applied to any Coulomb (charge interaction) +term that the potential calculates. The LJ factors are applied to the +remaining terms that the potential calculates, whether they represent +LJ interactions or not. The weighting factors are a scaling +pre-factor on the energy and force between the pair of atoms. A value +of 1.0 means include the full interaction; a value of 0.0 means +exclude it completely. The 1st of the 3 coefficients (LJ or Coulombic) is the weighting factor on 1-2 atom pairs, which are pairs of atoms directly bonded to