An improved semiempirical method for hydrated systems

Abstract

Hydrogen bonding is a key feature in many chemical and biochemical processes as well as in hydration phenomena. In previous works, it has been shown that description of hydrogen bonds by standard semiempirical methods is rather inaccurate and contains serious nonphysical artifacts. We have recently suggested a scheme to overcome this important limitation. Basically, we have proposed to replace the Gaussian correction function in the core-core interaction term of standard Austin model 1 (AM1) or parameterized model 3 (PM3) methods by a suitable function that is parameterized to correctly reproduce the long-range behavior of the interaction potential. A set of parameters for describing water-water interactions was derived using a highly refined ab initio potential energy surface for the water dimer. The present work extends that approach to the case of solute-solvent interactions of organic molecules in aqueous solution. Specifically, parameters for HH, HC, HN, HO, OC, ON and OO core-core terms are reported for use with the PM3 method. A series of tests for prototypical 1:1 complexes have been carried out and comparison with high-level ab initio results made. Errors in computed interaction energies are substantially smaller than those obtained in standard PM3 calculations, the root mean square decreasing from 3.41 to 1.74 kcal/mol. Artifacts in the potential energy surfaces (shoulders, spurious minima) present in PM3 are corrected with the new parameterization.