In previous work, a variational function that directly targets excited states based on their position in the energy spectrum and a polynomial-scaling Monte Carlo method for its evaluation and minimization delivered order-of-magnitude improvements in accuracy relative to equation of motion coupled cluster theory. [L. Zhao and E. Neuscamman, J. Chem. Theory Comput., 2016, 12 (8), 3436] As formulated, however, the functional was not guaranteed to be size-consistent. Therefore, the method cannot effectively model multi-molecular excited-state systems. By revising the variational function and the definition of the energy shift ω, we have recovered size-consistency and maintained the accuracy seen previously without sacrificing the generality of the method. The efficacy of the new functional is demonstrated on systems of small molecules that show the potential impact our method has on areas such as spectroscopy, green chemistry, and materials science.

Enforcing size-consistency in an excited state variational principle

254th National Meeting (2017)

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