TY - DATA T1 - Optimizing Conical Intersections without Derivative Coupling Vectors:  Application to Multistate Multireference Second-Order Perturbation Theory (MS-CASPT2)† PY - 2008/01/17 AU - Benjamin G. Levine AU - Joshua D. Coe AU - Todd J. Martínez UR - https://acs.figshare.com/articles/journal_contribution/Optimizing_Conical_Intersections_without_Derivative_Coupling_Vectors_Application_to_Multistate_Multireference_Second_Order_Perturbation_Theory_MS_CASPT2_sup_sup_/2962558 DO - 10.1021/jp0761618.s001 L4 - https://ndownloader.figshare.com/files/4661623 KW - multireference perturbation theory KW - multistate formulation KW - protein chromophore KW - method KW - sequential penalty KW - MECI geometries KW - Optimizing Conical Intersections KW - MRSDCI KW - energy conical intersections KW - intersection seam KW - optimization KW - benchmark multireference N2 - We introduce a new method for optimizing minimal energy conical intersections (MECIs), based on a sequential penalty constrained optimization in conjunction with a smoothing function. The method is applied to optimize MECI geometries using the multistate formulation of second-order multireference perturbation theory (MS-CASPT2). Resulting geometries and energetics for conjugated molecules including ethylene, butadiene, stilbene, and the green fluorescent protein chromophore are compared with state-averaged complete active space self-consistent field (SA-CASSCF) and, where possible, benchmark multireference single- and double-excitation configuration interaction (MRSDCI) optimizations. Finally, we introduce the idea of “minimal distance conical intersections”, which are points on the intersection seam that lie closest to some specified geometry such as the Franck−Condon point or a local minimum on the excited state. ER -