Calculation of Some Low-Lying Electronic Excitations of Barium Monofluoride Using the Eom-CC3 Method with an Effective Core Potential Approach

Barium monofluoride (BaF) is a polar molecule of interest to measurements of the electron electric dipole moment [1, 2]. For this purpose efforts are under way to investigate this molecule embedded within cryogenic matrices, e.g., in solid Ne [3]. For a theoretical understanding of the electronic structure of such an embedded molecule the need arises for efficient methods which are accurate, but also can handle a number of atoms which surround the molecule. The calculation for gas-phase BaF can be reduced to involve only outer electrons by representing the inner core of Ba with a pseudopotential [4] while carrying out a non-relativistic calculation with an appropriate basis set [5]. In this work we demonstrate to which extent this can be achieved using coupled-cluster methods to deal with electron correlation. As a test case the SrF(X 2Σ+ → B 2Σ+) transition is investigated and excellent accuracy is obtained with the EOM-CC3 method. For the BaF(X 2Σ+ → A′ 2∆, X 2Σ+ → A 2Π, X 2Σ+ → B 2Σ+) transitions various coupled-cluster approaches are compared with very good agreement for EOM-CC3 with experimentally derived spectroscopic parameters except for the excitation to the A′ 2∆ state for which the excitation energy is overestimated by 200 cm−1.