CANONICAL ORBITAL ENERGY DERIVATIVE STUDIES OF THE C2H2 AND H2CO GROUND-STATE POTENTIAL-ENERGY HYPERSURFACES

A study of first and second derivatives of the canonical orbital energ ies for the closed-shell self-consistent-field (SCF) wave-function has been extended to tetratomic molecular systems. The first derivatives of the orbital energies in terms of the Cartesian coordinate were dete rmined analytically and the second derivatives via the finite differen ce method, while the first and second derivatives of the electronic, n uclear and total energies were obtained analytically. At the stationar y points these energy derivatives were uniquely transformed from the C artesian to the normal coordinate system. Using the four equilibrium a nd three transition state structures of the closed-shell C2H2, : CCH2, H2CO and trans-HCOH molecules as examples, it is demonstrated that th e derivatives of the energies with respect to the normal coordinates p rovide useful chemical information concerning the molecular structures and reactivities. The orbital energy derivative method may be used as a powerful semi-quantitative model in understanding and interpreting various chemical phenomena.