Fast Atomic Charge Calculation for Implementation into a Polarizable Force Field and Application to an Ion Channel Protein

Table 2

Comparison of hydrogen-bonded dimer geometries and interaction energies to HF/6-31G data (this table is an extension of a web-based force field evaluation suite by Halgren [81–83] and compares the COSMOS-NMR force field with data provided by the web page http://server.ccl.net/cca/data/ff_evaluation_suite/).

Force field	Interaction energy [kcal/mol]	⋯ distance [Å]	-⋯ [°]
	Mean deviations
COSMOS-NMR	0.41	−0.04	10.6
MMFF94	−0.25	0.02	14.6
MMFF94s	−0.24	0.03	18.1
CFF95	1.10	0.21	27.0
CVFF	2.24	0.23	26.1
MSI CHARMM	0.60	0.08	34.0
CHARMM 22	0.00	0.05	15.0
OPLS	−0.49	0.02	22.9
AMBER	0.08	0.04	26.9
MM2	1.92	0.06	39.5
MM3	2.12	0.22	34.0

Each of the force fields handles all 66 hydrogen-bonded dimers except for (i) CVFF, for which the Cerius2 implementation could not perform the atom typing for imidazole, (ii) MM3, which lacks parameters for 12 of the dimers, and (iii) CHARMM 22, which lacked parameters for about half the systems even with extensions made locally. Some problems occurred with the interaction energies of two cyclic dimers that were not included in the comparison (oxalic acid/water, cyclic ammonia dimer) and three charged dimers (formamidinium/water, formaldehyde iminium/water, and bidentate/water) that show larger deviations of the interaction energies (≥2 kcal/mol).