forked from lijiext/lammps
doc page clarifications for CHARMM energy and dipole pre-factors
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@ -104,7 +104,15 @@ charmmfsw"_dihedral_charmm.html command. Eventually code from the new
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styles will propagate into the related pair styles (e.g. implicit,
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accelerator, free energy variants).
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The general CHARMM formulas are as follows
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NOTE: The newest CHARMM pair styles reset the Coulombic energy
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conversion factor used internally in the code, from the LAMMPS value
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to the CHARMM value, as if it were effectively a parameter of the
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force field. This is because the CHARMM code uses a slightly
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different value for the this conversion factor in "real
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units"_units.html (Kcal/mole), namely CHARMM = 332.0716, LAMMPS =
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332.06371. This is to enable more precise agreement by LAMMPS with
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the CHARMM force field energies and forces, when using one of these
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two CHARMM pair styles.
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: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
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torques do not act symmetrically. These formulas are discussed in
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"(Allen)"_#Allen2 and in "(Toukmaji)"_#Toukmaji2.
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Also note, that in the code, all of these terms (except Elj) have a
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C/epsilon prefactor, the same as the Coulombic term in the LJ +
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Coulombic pair styles discussed "here"_pair_lj.html. C is an
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energy-conversion constant and epsilon is the dielectric constant
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which can be set by the "dielectric"_dielectric.html command. The
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same is true of the equations that follow for other dipole pair
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styles.
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Style {lj/sf/dipole/sf} computes "shifted-force" interactions between
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pairs of particles that each have a charge and/or a point dipole
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moment. In general, a shifted-force potential is a (sligthly) modified
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