On the Validity of the Maximum Hardness and Minimum Polarizability Principles for Non-Totally Symmetric Vibrations

The zero-point static vibrational averaging (ZPVA) correction to the (hyper)polarizability is written in first-order as the sum of two contributions, one involving electric field derivatives, and the other a sum over normal coordinate derivatives of the zero point energy. It is shown that the sum over 3N-6 normal modes can be replaced by a single term using field-induced coordinates (FICs). A computational strategy that takes advantage of this simplification is presented and applied to a typical push-pull polyene NH2-(CH=CH)3-NO2. From the dependence of the first-order ZPVA on the field-dependent equilibrium geometry we also obtain other loworder static and dynamic vibrational curvature contributions to the (hyper)polarizabilities. The entire set of electronic and vibrational terms is partitioned into two different sequences, each of which exhibits rapid initial convergence for NH2(CH=CH)3NO2 at the Hartree-Fock/6-31G+p level. Including electron correlation at the MP2 level and the frequency-dependence of the ZPVA correction is discussed Support for this work under Grant PB98- 0457-C02-01 from the Dirección General de Enseñanza Superior e Investigación Científica y Técnica (MEC-Spain) is acknowledged