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git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@491 f3b2605a-c512-4ea7-a41b-209d697bcdaa

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sjplimp
2007-04-19 23:25:27 +00:00
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26
doc/pair_modify.txt
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@ -43,13 +43,15 @@ not affected by this setting.
The {mix} keyword affects how Lennard-Jones coefficients for epsilon
and sigma are generated for interactions between atoms of type I and
J, when I != J. (I = J coefficients are set explicitly in the data
file or input script.) The "pair_coeff"_pair_coeff.html command can
be used in the input script to specify epilon/sigma for a specific I,J
pairing, which overrides the setting of the {mix} keyword. In each
case, the LJ cutoff is mixed the same way as sigma.
J, when I != J. Coefficients for I = J are set explicitly in the data
file or input script. The "pair_coeff"_pair_coeff.html command can be
used in the input script to specify epilon/sigma for a specific I != J
pairing, which overrides the setting of the {mix} keyword.
These are the formulas used by the 3 {mix} options:
These are the formulas used by the 3 {mix} options. In each case, the
LJ cutoff is mixed the same way as sigma. Note that some of these
options are not available for certain pair styles. See the doc page
for individual pair styles for those restrictions.
{geometric}
@ -65,17 +67,7 @@ sigma_ij = (sigma_i + sigma_j) / 2 :pre
epsilon_ij = (2 * sqrt(epsilon_i*epsilon_j) * sigma_i^3 * sigma_j^3) /
(sigma_i^6 + sigma_j^6)
sigma_ij= ((sigma_i**6 + sigma_j**6) / 2) ^ (1/6) :pre
Style {soft} only uses a pre-factor coefficient, which is always mixed
geometrically, regardless of the {mix} setting. The {charmm} styles
are always mixed arithmetically, regardless of the {mix} setting. The
{class2} styles are always mixed as a sixthpower, regardless of the
{mix} setting, except that the cutoff is mixed according to the mix
setting. Style {lj/expand} always mixes its delta coefficient using
the rule
delta_ij = (delta_i + delta_j) / 2 :pre
sigma_ij = ((sigma_i**6 + sigma_j**6) / 2) ^ (1/6) :pre
The {table} keyword applies to pair styles with a long-range Coulombic
term (lj/cut/coul/long and lj/charmm/coul/long). If N is non-zero, a