Relativistic and correlated calculations on the ground and excited states of ThO

Abstract

We report on the performance of the third-order Douglas–Kroll ab initio model potential (DK3-AIMP) method-based electron-correlated spin–orbit calculations. Our treatment assumes that the problem can be separated into a spin–free correlation treatment and a spin–orbit calculation. The correlation effects were calculated using the multistate complete active space second-order perturbation method, and the spin–orbit effects were treated by means of the restricted active space state interaction spin–orbit method, where the spin–orbit effects were approximated by the Douglas–Kroll type of atomic mean-field spin–orbit method. We used our method for illustrative calculations on the ground and low-lying electronic states of thorium monoxide. For a proper description of the inner core region in the spin–orbit calculations, an auxiliary spin–orbit basis set was introduced. The DK3-AIMP-based electron-correlated spin–orbit calculations on ThO yield good agreement with corresponding all-electron results and with the available experimental data. This confirms that the DK3-AIMP method can be easily combined with highly accurate correlation treatments and relativistic effects, both of which are vital for studying the actinides. To our knowledge, the literature contains no references to AIMP calculations on the low-lying states of ThO.

Communication: Theoretical study of ThO for the electron electric dipole moment search

“…21 Our calculations show that being presented in the S coupling scheme, the spin-orbit mixed H state of ThO has the main contribution (more than 95%) from the 3 1 configurations (see also Ref. 16). Therefore, due to the identity 3 1 |S e + | n0 ± ≡ 0, where S e is the electronic spin operator, for pure S state, the inequality | H 3 1 |S e + | n0 ± | 1 holds with a good accuracy.…”

“…5, 14-16 First estimates of E eff in the 16. In the present paper we concentrate on the precise two-component relativistic coupled clusters calculations of the complementary data (E eff , W T ,P ) which are most relevant for the direct interpretation of ThO experiment in terms of the electron EDM and constant of T,P-odd pseudoscalar-scalar electron-nucleus interaction.…”

Molecular structure and thermodynamic properties of the gaseous ThC2 and ThC4 species

“…According to a recent comprehensive computational study of ThO, the Th 2+ ion has a singlet ground state in that molecule [21]. On the basis of this we also expected that the singlet states of ThC 2 and ThC 4 are more stable than the triplet states.…”

Communication: Electric properties of the ThO(X Σ1+) molecule

“…Marian et al 6 and Küchle et al 7 provided evidence that the scalar relativistic effects can be successfully accounted for using the relativistic pseudopotentials. Multireference calculations by Küchle et al 7 and Paulovič et al 8 indicated that the single-reference treatment would be appropriate at equilibrium and that the vectorial spin-orbit coupling results in less than 1% admixture of electronically excited states. This opens the possibility of using powerful single-reference techniques, e.g., the coupled cluster method, to study the electric properties.…”