ANALYTICAL FIRST AND 2ND ENERGY DERIVATIVES OF THE GENERALIZED CONDUCTORLIKE SCREENING MODEL FOR FREE-ENERGY OF SOLVATION

We present analytical expressions for the first and second energy derivatives of our recently proposed generalized conductorlike screening model (GCOSMO) for free energy of solvation of solute in an arbitrary shape cavity. An application to study hydration effects on structure and stability of glycine zwitterion in aqueous solution is also presented. These calculations were carried out at the Hartree-Fock, second-order Moller-Plesset perturbation theory and different nonlocal density functional theory levels using the 6-31G(d,p) basis set. We found that our quantum mechanical GCOSMO solvation model costs from 10% to 40% extra cpu time per one Berny optimization step compared to the gas-phase calculations for different levels of theory. For the glycine system, the optimized zwitterionic structure in aqueous solution agrees very well with experimental crystal structure and the enthalpy change for transfering glycine from the gas phase to the aqueous solution is also in excellent agreement with experimental data, The ''single point'' approach, which has been used in the past, yields erroneous results. The efficiency and accuracy of our GCOSMO solvation model indicate that this model can be a practical tool for studying structure and activity of moderately large biological systems in solutions. (C) 1995 American Institute of Physics.