An open-shell restricted Hartree—Fock perturbation theory based on symmetric spin orbitals

✍ Scribed by Timothy J. Lee; Dylan Jayatilaka

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 850 KB
• Volume: 201
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(93)85024-i

✦ Synopsis

A new open-shell perturbation theory is formulated in terms of symmetric spin orbitals. Only one set of spatial orbitals is required, thereby reducing the number of independent coeffmients in the perturbed wavefunctions. For second order, the computational cost is shown to be similar to a closed-shell calculation. This formalism is therefore more efficient than the recently developed RMP, ROMP or RMP-MBPT theories. The perturbation theory described herein was designed to have a close correspondence with our recently proposed coupled-cluster theory based on symmetric spin orbitals. The tirst-order wrvefnnction contains contributions from only doubly excited determinants. Equilibrium structures and vibrational frequencies determined from second-order perturbation theory are presented for OH, NH, CH, Os, NHs and CHs.