Ab initio computation of d-d excitation energies in low-dimensional Ti and V oxychlorides

TL;DR

This study uses ab initio quantum chemical methods to accurately compute d-d excitation energies in TiOCl and VOCl, revealing significant orbital splitting and providing predictions for future experimental validation.

Contribution

The paper introduces a cluster-in-solid computational scheme to calculate d-d excitations in low-dimensional transition metal oxychlorides, with results aligning well with experimental data.

Findings

Lowest-energy d-d excitations are within the t2g subshell, starting at 0.34 eV.

Spin triplet to singlet excitations in VOCl are about 1 eV higher.

Predicted d-d excitation energies and symmetries for VOCl await experimental verification.

Abstract

Using a quantum chemical cluster-in-solid computational scheme, we calculate the local d-d excitation energies for two strongly correlated Mott insulators, the oxychlorides TiOCl and VOCl. TiOCl harbors quasi-one-dimensional spin chains made out of S = 1/2 Ti3+ ions while the electronic structure of VOCl displays a more two-dimensional character. We find in both cases that the lowest-energy d-d excitations are within the t2g subshell, starting at 0.34 eV and indicating that orbital degeneracies are significantly lifted. In the vanadium oxychloride, spin triplet to singlet excitations are calculated to be 1 eV higher in energy. For TiOCl, the computed d-level electronic structure and the symmetries of the wavefunctions are in very good agreement with resonant inelastic x-ray scattering results and optical absorption data. For VOCl, future resonant inelastic x-ray scattering experiments will constitute a direct test of the symmetry and energy of about a dozen of different d-d excitations that we predict here.