The Spin-Flip Variant of the Algebraic-Diagrammatic Construction Yields the Correct Topology of S1/S0 Conical Intersections

Daniel Lefrancois; Deniz Tuna; Todd J Martínez; Andreas Dreuw

doi:10.1021/acs.jctc.7b00634

The Spin-Flip Variant of the Algebraic-Diagrammatic Construction Yields the Correct Topology of S₁/S₀ Conical Intersections

J Chem Theory Comput. 2017 Sep 12;13(9):4436-4441. doi: 10.1021/acs.jctc.7b00634. Epub 2017 Aug 31.

Authors

Daniel Lefrancois¹, Deniz Tuna², Todd J Martínez^{3

4}, Andreas Dreuw¹

Affiliations

¹ Interdisciplinary Center for Scientific Computing, Ruprecht-Karls University , Im Neuenheimer Feld 205, 69120 Heidelberg, Germany.
² Max-Planck-Institut für Kohlenforschung , 45470 Mülheim an der Ruhr, Germany.
³ Department of Chemistry and The PULSE Institute, Stanford University , Stanford, California 94305, United States.
⁴ SLAC National Accelerator Laboratory , Menlo Park, California 94025, United States.

PMID: 28742963
DOI: 10.1021/acs.jctc.7b00634

Abstract

While the conventional variants of the algebraic-diagrammatic construction (ADC) scheme for the polarization propagator are generally incapable of correctly describing the topology of S₁/S₀ conical intersections (CIs), its corresponding spin-flip (SF) variant of third-order ADC (ADC(3)) is herein demonstrated to successfully reproduce the S₁/S₀ minimum-energy CI (MECI) of twisted formaldinium (H₂C═NH₂⁺). Analytical nuclear excited-state gradients of ADC have been used in combination with the CIOpt program for the optimization of the MECI without the need for nonadiabatic-coupling vectors. For comparison, MS-CASPT2 calculations were performed via conventional CI optimization employing analytical nonadiabatic-coupling vectors. It is shown that SF-ADC(3) yields the correct dimensionality of the CI and overall compares very favorably to the MS-CASPT2 results.