Investigation of the Jahn-Teller Transition in TiF3 using Density Functional Theory

TL;DR

This study uses density functional theory to analyze the electronic, magnetic, and structural properties of TiF3, revealing the importance of electron correlations and dipole interactions in the Jahn-Teller transition.

Contribution

It demonstrates that electron correlations beyond LDA are crucial for understanding the Jahn-Teller transition in TiF3, and predicts an orbitally ordered insulating ground state using LDA+U.

Findings

LDA predicts a ferromagnetic metal, not matching experiments.

LDA+U predicts an antiferromagnetic insulator with orbital order.

The estimated exchange constant is approximately 24 K.

Abstract

We use first principles density functional theory to calculate electronic and magnetic properties of TiF3 using the full potential linearized augmented plane wave method. The LDA approximation predicts a fully saturated ferromagnetic metal and finds degenerate energy minima for high and low symmetry structures. The experimentally observed Jahn-Teller phase transition at Tc=370K can not be driven by the electron-phonon interaction alone, which is usually described accurately by LDA. Electron correlations beyond LDA are essential to lift the degeneracy of the singly occupied Ti t2g orbital. Although the on-site Coulomb correlations are important, the direction of the t2g-level splitting is determined by the dipole-dipole interactions. The LDA+U functional predicts an aniferromagnetic insulator with an orbitally ordered ground state. The input parameters U=8.1 eV and J=0.9 eV for the Ti 3d orbital were found by varying the total charge on the TiF$_6^{2-}$ ion using the molecular NRLMOL code. We estimate the Heisenberg exchange constant for spin-1/2 on a cubic lattice to be approximately 24 K. The symmetry lowering energy in LDA+U is about 900 K per TiF3 formula unit.