Theoretical spectroscopy of organic systems

The complete active space (CAS) SCF method in conjunction with the multicon figurational second-order perturbation theory (CASPT2) has been applied to study the electronically excited states of basic organic compounds. As show n in the lecture with a number of examples, the CASPT2 method is capable of yielding accurate results for relative energies and other properties of ex cited states, provided that flexible one-electron basis sets are employed. The applications comprise an ample range of systems and problems, including polyenes, conjugated and unconjugated dienes, alternant and nonalternant h ydrocarbons, polyenals, etc. As a whole these studies enable both qualitati ve and quantitative understanding of electronic spectra of organic molecule s of fundamental importance. (C) 1999 Elsevier Science B.V. All rights rese rved.