Analytical Derivative Coupling for Multistate CASPT2 Theory

Jae Woo Park*, Toru Shiozaki

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

45 Scopus citations


The probability of nonradiative transitions in photochemical dynamics is determined by the derivative couplings, the couplings between different electronic states through the nuclear degrees of freedom. Efficient and accurate evaluation of the derivative couplings is, therefore, of central importance to realize reliable computer simulations of photochemical reactions. In this work, the derivative couplings for multistate multireference second-order perturbation theory (MS-CASPT2) and its "extended" variant (XMS-CASPT2) are studied, in which we present an algorithm for their analytical evaluation. The computational costs for evaluating the derivative couplings are essentially the same as those for calculating the nuclear energy gradients. The geometries and energies calculated with XMS-CASPT2 for small molecules at minimum energy conical intersections (MECIs) are in good agreement with those computed by multireference configuration interaction. As numerical examples, MECIs are optimized using XMS-CASPT2 for stilbene and a green fluorescent protein model chromophore (the 4-para-hydroxybenzylidene-1,2-dimethyl-imidazolin-5-one anion).

Original languageEnglish (US)
Pages (from-to)2561-2570
Number of pages10
JournalJournal of Chemical Theory and Computation
Issue number6
StatePublished - Jun 13 2017

ASJC Scopus subject areas

  • Computer Science Applications
  • Physical and Theoretical Chemistry

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