Abstract
It is shown that the convergence of anharmonic infrared spectral intensities with respect to the basis set size is much enhanced in explicitly correlated calculations as compared to traditional configuration interaction type wave function expansion. Explicitly correlated coupled cluster (CC) calculations using Slater-type geminal correlation factor (CC-F12) yield well-converged dipole derivatives and vibrational intensities for hydrogen fluoride with basis set involving f functions on the heavy atom. Combination of CC-F12 with singles, doubles, and non-iterative triples (CCSD(T)-F12) with small corrections due to quadruple excitations, core-electron correlation, and relativistic effects yields vibrational line positions, dipole moments, and transition dipole matrix elements in good agreement with the best experimental values.
Highlights
Communication: Convergence of anharmonic infrared intensities of hydrogen fluoride in traditional and explicitly correlated coupled cluster calculations
It is well known that the accuracy of quantum chemically calculated spectroscopic properties is largely limited by three factors: (i) approximate expansion of the electronic wave function in the basis of one-electron functions, (ii) approximate treatment of electron correlation, and (iii) treatment of anharmonicity in the potential energy and property surfaces
Given the excellent performance of explicitly correlated methods in calculating molecular geometries, vibrational frequencies, and dipole moments, we decided to investigate their performance for infrared spectral intensities, which depend on dipole moment derivatives
Summary
Communication: Convergence of anharmonic infrared intensities of hydrogen fluoride in traditional and explicitly correlated coupled cluster calculations. Given the excellent performance of explicitly correlated methods in calculating molecular geometries, vibrational frequencies, and dipole moments, we decided to investigate their performance for infrared spectral intensities, which depend on dipole moment derivatives.
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