Characterization of the S1-S2 conical intersection in pyrazine using ab initio multiconfiguration self-consistent-field and multireference configuration-interaction methods

Clemens Woywod, Wolfgang Domcke, Andrzej L. Sobolewski, Hans Joachim Werner

Research output: Contribution to journalArticlepeer-review

208 Scopus citations

Abstract

Potential-energy surfaces of the three lowest singlet states of pyrazine have been calculated as a function of ab initio determined ground-state normal coordinates, using complete-active-space self-consistent-field (CASSCF) and multireference configuration interaction (MRCI) techniques. The conical intersection of the S1 and S2 adiabatic potential-energy surfaces has been mapped out in selected subspaces spanned by the most relevant vibrational coordinates. A unitary transformation from the adiabatic to a quasidiabatic electronic representation is performed, which eliminates the rapid variations of the wave functions responsible for the singularity of the nonadiabatic coupling element. Transition-dipole-moment functions have been obtained in the adiabatic and in the diabatic representation. The leading coefficients of the Taylor expansion of the diabatic potential-energy and transition-dipole-moment surfaces in terms of ground-state normal coordinates at the reference geometry have been obtained at the CASSCF/MRCI level. Using a vibronic-coupling model Hamiltonian based on this Taylor expansion, the absorption spectrum of the interacting S1-S2 manifold has been calculated, taking account of the four spectroscopically most relevant modes.

Original languageEnglish
Pages (from-to)1400-1413
Number of pages14
JournalJournal of Chemical Physics
Volume100
Issue number2
DOIs
StatePublished - 1994

Fingerprint

Dive into the research topics of 'Characterization of the S1-S2 conical intersection in pyrazine using ab initio multiconfiguration self-consistent-field and multireference configuration-interaction methods'. Together they form a unique fingerprint.

Cite this