Table 2.

Atomic charges and polarizability for DMP calculated using the original and refined CHEQ force fields compared to ab initio computed MP2/cc-pVTZ values

Atomic charge	CHARMM (fixed-charge)	CHEQ (original)	CHEQ (refined)	MP2/cc-pVTZ
P1	1.500	1.278	1.315	1.339
O3	−0.780	−0.783	−0.864	−0.834
O4	−0.780	−0.783	−0.864	−0.834
O1	−0.570	−0.389	−0.563	−0.500
O2	−0.570	−0.389	−0.563	−0.500
C1	−0.170	−0.033	0.207	0.210
H11	0.090	0.022	0.019	−0.030
H12	0.090	0.011	0.041	−0.020
H13	0.090	0.033	0.002	0.005
C2	−0.170	−0.033	0.207	0.210
H21	0.090	0.033	0.002	0.005
H22	0.090	0.022	0.019	−0.030
H23	0.090	0.011	0.041	−0.020
Polarizability (Å3)	n/a	13.587	8.057	8.786

Ab initio values were computed at the MP2/cc-pVTZ level of theory using Gaussian 03. The fixed charges used in the nonpolarizable CHARMM force field are also shown.