Table 5.

Interaction energies for complexes of DMP with water

	Interaction energy (kcal/mol)
	Original CHEQ	Refined CHEQ	MP2/cc−pVTZ
Complex 1	−13.04	−14.34	−15.01
Complex 2	−12.65	−15.72	−15.62

Energies computed at the MP2/cc-PVTZ level of theory using Gaussian 03 are compared to those calculated using the original and revised CHEQ models in CHARMM. Complex 1 has the water hydrogen-bonded to one bridging oxygen and one double-bonded oxygen of the phosphate, and complex 2 has the water hydrogen bonded to both double-bonded oxygens of the phosphate.