ANALYT (W)

By default, finite difference derivatives of energy with respect to geometry are used. If ANALYT is specified, then analytical derivatives are used instead. Since the analytical derivatives are over Gaussian functions--a STO-6G basis set is used--the overlaps are also over Gaussian functions. This will result in a very small (less than 0.1 kcal/mole) change in heat of formation. Use analytical derivatives (a) when the mantissa used is less than about 51-53 bits, or (b) when comparison with finite difference is desired. Finite difference derivatives are still used when non-variationally optimized wavefunctions are present.