ANALYTICAL 2ND DERIVATIVES OF THE FREE-ENERGY IN SOLUTION BY POLARIZABLE CONTINUUM MODELS

We present an algorithm for the analytical evaluation of flee energy s econd derivatives with respect to nuclear displacements in the framewo rk of the polarizable continuum model (PCM). The algorithm has been ob tained for two recently proposed PCM versions, namely the conductor-li ke and the isotropic integral equation formalism models, and it can be applied to Hartree-Fock and to density functional SCF calculations on closed- and open-shell systems. The formal derivation is shown in det ail and a number of numerical tests are presented: the applications sh ow that analytical results are in excellent agreement with those obtai ned numerically and, as in vacuo, the analytical procedure is far more efficient. The presented algorithm can be routinely used with an upco ming release of the Gaussian program. (C) 1998 American Institute of P hysics. [S0021-9606(98)30838-7].