Potential-derived point-charge model study of electrostatic interaction energies in some hydrogen-bonded systems

Mulliken's atomic changes (MC) and potential derived (PD) point charges obtained from STO-3G wave functions are used to study the electrostatic interaction energies for a series of representative hydrogen-bonded complexes. The results of the above-mentioned models are compared with the more accurate results of segmental multipole moment (SMM) expansion, and it is shown that the PD model is superior to the MC model. The results of PD model are shown to be well correlated with the results of SMM expansion technique. Results of our calculations using 6-31G and 6-31G** PD charges are also reported here. Electrostatic interaction energies obtained using 6-31G** PD charges are compared with the 6-31G** SCF interaction energies available for the nine hydrogen-bonded dimers of ammonia, water, and hydrogen fluoride and a good correlation between the two is shown. The interrelationship between the results of different basis sets are also examined for the PD point-charge model. The electrostatic interaction energies obtained using STO-3G PD model are shown to be well correlated to the results of 6-31G and 6-31G** PD models.