Programme

I.13 -- Invited, VCTP-51

Date: Thursday, 6 August 2026

Time: 14:00 - 14:40

Cluster Quantum-Chemical Approach to Studying Electronic and Magnetic properties of Complex Transition Metal Oxides

Liudmila Siurakshina

Meshcheryakov Laboratory of Information Technologies, JINR, Dubna, Russia

Synthesis of new functional materials based on transition metal (TM) oxides poses new challenges in the theoretical description of their electronic and magnetic properties, taking into account the effects of strong electron correlations. At the core of this challenge is the formulation and numerical justification of multiorbital Hubbard models, as well as their low-energy limit in the form of effective spin Hamiltonians. The models are aimed at the quantitative description of complex oxides of TM elements placed in three consecutive rows of the periodic table and showing the increasing spin-orbit coupling within the unfilled nd-electron shells, n = 3, 4, 5. To address this problem, we proposed and developed an ab initio quantum-chemical method for calculating the local electronic structure (N-electron wave functions and their energies) of small crystalline fragments (clusters) of complex oxides of all three families of TMs. To account for the effects of strong electron correlations, the multielectron states of the cluster obtained at the first stage in the Hartree-Fock (HF) approximation are further refined and expanded at the stage of post-HF calculations of increasing complexity. The final numerical results determine the quantitative estimates for a set of interaction constants of the above-mentioned Hubbard and spin models. Applications of ab initio cluster calculations are given for the quantitative description of (i) the spectra of local multiplet states of electrons in a crystal field measured in copper and vanadium oxides by RIXS spectroscopy, (ii) the phenomenon of thermally induced spin transitions in cobalt oxides and (iii) superexchange interactions of pseudospins (Kramers doublet states) in iridium oxides with strong spin-orbit interactions [1-3]. 1. V. Katukuri, V. Yushankhai, L. Siurakshina, J. Brink, L. Hozoi, I. Rousochatzakis. Mechanism of Basal-Plane Antiferromagnetism in the Spin-Orbit Driven Iridate Ba2IrO4. Physical Review X. 4. (2014). 2. L.A. Siurakshina, V.Y. Yushankhai. Anisotropic Spin Models of Iridium Oxides: Justification by a Cluster Quantum-Chemical Approach. Bull. Russ. Acad. Sci. Phys. 89, 1802–1808 (2025). 3. L. Siurakshina. Superexchange model for the planar iridate Ba2IrO4 : From an analytical approach to ab initio quantum-chemical computations. Phys. Rev. B (in press, 2026).

Presenter: Siurakshina Liudmila