title: Optimizing conical intersections by spin-flip density functional theory: application to ethylene.
abstract: Conical intersections (CIs) of ethylene have been successfully determined using spin-flip density functional theory (SFDFT) combined with a penalty-constrained optimization method. We present in detail three structures, twisted-pyramidalized, hydrogen-migrated, and ethylidene CIs. In contrast to the linear response time-dependent density functional theory, which predicts a purely twisted geometry without pyramidalization as the S(1) global minimum, SFDFT gives a pyramidalized structure. Therefore, this is the first correct optimization of CI points of twisted ethylene by the DFT method. The calculated energies and geometries are in good agreement with those obtained by the multireference configuration interaction (MR-CI) method and the multistate formulation of second-order multireference perturbation theory (MS-CASPT2).
authors.affiliation: Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Minezawa
authors.forename: Mark S
authors.initials: MS
authors.lastname: Gordon
mesh_terms: D003198:Computer Simulation; D005030:Ethylenes / Q000737:chemistry*; D008956:Models, Chemical; D010777:Photochemistry; D011789:Quantum Theory; D013997:Time Factors
chemical_list: D005030:Ethylenes; C036216:ethylene