doc page clarifications for CHARMM energy and dipole pre-factors

This commit is contained in:
Steve Plimpton 2017-06-23 15:54:14 -06:00
parent 25a5d12af3
commit 4fcbd58d5a
2 changed files with 17 additions and 1 deletions

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@ -104,7 +104,15 @@ charmmfsw"_dihedral_charmm.html command. Eventually code from the new
styles will propagate into the related pair styles (e.g. implicit,
accelerator, free energy variants).
The general CHARMM formulas are as follows
NOTE: The newest CHARMM pair styles reset the Coulombic energy
conversion factor used internally in the code, from the LAMMPS value
to the CHARMM value, as if it were effectively a parameter of the
force field. This is because the CHARMM code uses a slightly
different value for the this conversion factor in "real
units"_units.html (Kcal/mole), namely CHARMM = 332.0716, LAMMPS =
332.06371. This is to enable more precise agreement by LAMMPS with
the CHARMM force field energies and forces, when using one of these
two CHARMM pair styles.
:c,image(Eqs/pair_charmm.jpg)

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@ -71,6 +71,14 @@ and force, Fij = -Fji as symmetric forces, and Tij != -Tji since the
torques do not act symmetrically. These formulas are discussed in
"(Allen)"_#Allen2 and in "(Toukmaji)"_#Toukmaji2.
Also note, that in the code, all of these terms (except Elj) have a
C/epsilon prefactor, the same as the Coulombic term in the LJ +
Coulombic pair styles discussed "here"_pair_lj.html. C is an
energy-conversion constant and epsilon is the dielectric constant
which can be set by the "dielectric"_dielectric.html command. The
same is true of the equations that follow for other dipole pair
styles.
Style {lj/sf/dipole/sf} computes "shifted-force" interactions between
pairs of particles that each have a charge and/or a point dipole
moment. In general, a shifted-force potential is a (sligthly) modified