title: Second-order perturbation theory with complete and restricted active space reference functions applied to oligomeric unsaturated hydrocarbons.
abstract: Multiconfigurational second-order perturbation theory based on either a complete active space reference wave function (CASSCF/CASPT2) or a restricted active space reference wave function (RASSCF/RASPT2) has been applied to compute one-electron ionization potentials and vertical electronic energy differences of oligomers of length n formed from ethylene (n = 1-10), acetylene (n = 1-5), and phenylene (n = 1-3) subunits. The RASSCF/RASPT2 approach offers an accuracy similar to CASSCF/CASPT2 at significantly reduced computational expense (both methods show good agreement with experimental data where available). It is shown that RASPT2 extends the range of CASPT2-like approaches by permitting the use of larger active spaces.
authors.affiliation: Department of Physical Chemistry, University of Geneva, 30q. E. Ansermet, 1211 Genève, Switzerland.
authors.forename: Abdul Rehaman
authors.initials: AR
authors.lastname: Moughal Shahi
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Cramer
authors.forename: Laura
authors.initials: L
authors.lastname: Gagliardi