Examining the ground- and excited-state potential energy surfaces with Spin-Flip ORMAS: Minima, Saddle Points, and Conical Intersections
Joani Mato1 , Mark S. Gordon1
Iowa State University
Email: jmato@iastate.edu
The recently introduced Spin-Flip (SF) ORMAS method and its analytic nuclear gradient are used to study chemical processes in the ground and excited states. SF-ORMAS offers all the benefits of traditional SF-CI methods – such as non-dynamic correlation, size-consistency, and variational upper-bounds – in addition to maintaining the correct spin-symmetry. Moreover, SFORMAS allows for flexible and diverse wave functions due to its ability to freely partition the orbital space. Thus, numerous Spin-Flip schemes are possible. As a proof of principle, we use SF-ORMAS to study the ground and excited-state potential energy surfaces of azomethane, comparing results to those of more expensive multi-reference methods. We examine the cistrans isomerization reaction paths and their relation to the S0/S1 conical intersection of azomethane. Explicit solvent effects are also examined through the interface of SF-ORMAS with the Effective Fragment Potential (EFP) method. We demonstrate that SF-ORMAS is qualitatively comparable to multi-reference methods such as CASSCF, MR-CI, and MRPT2.