Understanding excited electronic states is essential in many fields such as photovoltaics, synthetic chemistry, and more. Despite multiple breakthroughs in computational technology and developments in excited-state theories and methodologies, the study of potential energy surfaces and high-order properties using excited-state models based on response theory or configuration interaction-based approaches remains computationally intensive and can be cost-prohibitive for even modest-sized systems. An alternative approach seeks excited state solutions using self-consistent field (SCF) calculations. Such SCF calculations often require special treatment to avoid collapse to the variational ground state and to drive the SCF engine toward a solution that is representative of the desired excited state. In this work, one of these SCF driver methods, the projected initial maximum overlap method (PIMOM), is used to exploit SCF methods for exploring molecular vibrational modes in excited electronic states. A test set of molecules is investigated and compared with results obtained using time-dependent density functional theory and configuration interaction with single substitutions. Spin-purification is used to remedy spin-contamination effects where needed. Overall, the combination of PIMOM-guided SCF calculations with spin-purification yields a practical approach for exploring and characterizing excited electronic state vibrational spectra.

Good vibrations: Calculating excited state frequencies using ground state self-consistent field models

ACS Spring Meeting 2021

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