Low-lying electronic terms of diatomic molecules AB (A = Sc–Ni, B = Cu/Ag/Au)

Abstract

Low-lying electronic terms of 24 heteronuclear diatomic molecules AB (A = Sc–Ni, B = Cu/Ag/Au) have been systematically studied. Scalar relativistic effects were included by use of the spin-free Douglas–Kroll–Hess (DKH) Hamiltonian. The complete active space self-consistent field (CASSCF) method, followed by multi-reference configuration interaction (MRCI), was used to construct full potential energy curves (PECs). Spectroscopic constants as well as dipole moments are also reported. Spin-orbit coupling was subsequently calculated perturbatively via the spin-orbit terms of the Breit–Pauli Hamiltonian based on the CASSCF wavefunctions. Full spin-orbit coupled PECs were thus constructed for the low-lying terms of NiCu and NiAg. In addition, Kramers-restricted configuration interaction (KRCI) with the exact 2-component (X2C) Hamiltonian was utilised for the atoms and for the Cu-containing diatomic molecules. The influence of relativistic effects, spin-orbit coupling, core correlation effects and basis set incompleteness was probed for some selected cases. It is shown that for 23 out of the 24 diatomic molecules considered here a direct correspondence exists between the ground state terms (GSTs) of the monocations $A^{+}\left(\right(3\mathrm{d}4\mathrm{s}{)}^{m-12S+1}{L}_J,m=3\left(\mathrm{S}\mathrm{c}\right)-10\left(\mathrm{N}\mathrm{i}\right))$ and those of the diatomic molecules $AB\left(\right(\sigma \sigma \sigma \pi \delta {)}^{m+1}{X}^{2S^{\mathrm{\prime }}+1}{\mathrm{\Lambda }}_{\mathrm{\Omega }})$ with $S^{\mathrm{\prime }}=S,\mathrm{\Lambda }=L$ and $\mathrm{\Omega }=J$.

GRAPHICAL ABSTRACT

Keywords:

• Ground and low-lying excited states
• 3d transition metal atoms
• coinage metal atoms
• heteronuclear diatomic molecules
• Λ–S terms
• spin-orbit coupling

Acknowledgments

We gratefully acknowledge funding received from the German Academic Exchange Service (Deutscher Akademischer Austausch Dienst, DAAD) under Grant ID 57129429. Without this generous support the scientific work and the thesis [142], on which the work presented here is based, would be non-existent. We like to thank all staff of the High-Performance Computing (HPC) facilities at Freie Universität Berlin (ZEDAT), in particular Dr Boris Proppe and Dr Loris Bennett, for their invaluable work. D.A.S. wishes to acknowledge Dr Lukas Eugen Marsoner Steinkasserer for helpful discussions. We thank the two anonymous reviewers for the constructive criticism of our work.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the German Academic Exchange Service (Deutscher Akademischer Austausch Dienst, DAAD) [grant number 57129429].