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 deri vatives of our recently proposed generalized conductorlike screening m odel (GCOSMO) for free energy of solvation of solute in an arbitrary s hape cavity. An application to study hydration effects on structure an d stability of glycine zwitterion in aqueous solution is also presente d. These calculations were carried out at the Hartree-Fock, second-ord er Moller-Plesset perturbation theory and different nonlocal density f unctional theory levels using the 6-31G(d,p) basis set. We found that our quantum mechanical GCOSMO solvation model costs from 10% to 40% ex tra 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 w ell with experimental crystal structure and the enthalpy change for tr ansfering glycine from the gas phase to the aqueous solution is also i n excellent agreement with experimental data, The ''single point'' app roach, which has been used in the past, yields erroneous results. The efficiency and accuracy of our GCOSMO solvation model indicate that th is model can be a practical tool for studying structure and activity o f moderately large biological systems in solutions. (C) 1995 American Institute of Physics.