Jw. Storer et al., CLASS-IV CHARGE MODELS - A NEW SEMIEMPIRICAL APPROACH IN QUANTUM-CHEMISTRY, Journal of computer-aided molecular design, 9(1), 1995, pp. 87-110
We propose a new criterion for defining partial charges on atoms in mo
lecules, namely that physical observables calculated from those partia
l charges should be as accurate as possible. We also propose a method
to obtain such charges based on a mapping from approximate electronic
wave functions. The method is illustrated by parameterizing two new ch
arge models called AM1-CM1A and PM3-CM1P, based on experimental dipole
moments and, respectively, on AM1 and PM3 semiempirical electronic wa
ve functions. These charge models yield rms errors of 0.30 and 0.26 D,
respectively, in the dipole moments of a set of 195 neutral molecules
consisting of 103 molecules containing H, C, N and O, covering variat
ions of multiple common organic functional groups, 68 fluorides, chlor
ides, bromides and iodides, 15 compounds containing H, C, Si or S, and
9 compounds containing C-S-O or C-N-O linkages. In addition, partial
charges computed with this method agree extremely well with high-level
ab initio calculations for both neutral compounds and ions. The CM1 c
harge models provide a more accurate point charge representation of th
e dipole moment than provided by most previously available partial cha
rges, and they are far less expensive to compute.