Quantification of the Ionic Character of Multiconfigurational Wave Functions: The Q_a^t Diagnostic.

ABSTRACT: The complete active space self-consistent field (CASSCF) method is a cornerstone in modern excited-state quantum chemistry providing the starting point for most common multireference computations. However, CASSCF, when used with a minimal active space, can produce significant errors (>2 eV) even for the excitation energies of simple hydrocarbons if the states of interest possess ionic character. After illustrating this problem in some detail, we present a diagnostic for ionic character, denoted as Q _a^t, that is readily computed from the transition density. A set of 11 molecules is considered to study errors in vertical excitation energies. State-averaged CASSCF obtains a mean absolute error (MAE) of 0.87 eV for the 34 singlet states considered. We highlight a s

SUBMITTER: do Monte SA 

PROVIDER: S-EPMC10683019 | biostudies-literature | 2023 Nov

REPOSITORIES: biostudies-literature