First-Principles investigation of the First-order Phase Transition in Kagome Na$_2$Ti$_3$Cl$_8$

TL;DR

This study uses first-principles calculations to analyze the structural and electronic changes in Na$_2$Ti$_3$Cl$_8$ during its first-order phase transition, revealing a trimerization of Ti ions and a significant energy barrier.

Contribution

It provides a detailed first-principles analysis of the phase transition and electronic structure of Na$_2$Ti$_3$Cl$_8$, highlighting the role of Ti trimerization and energy barriers.

Findings

Successful reproduction of crystal structures with Hubbard correction

Identification of an 80 meV energy barrier for the phase transition

Electronic analysis shows direct Ti-Ti metal bonding in the low-temperature phase

Abstract

The antiferromagnetic kagome material Na2Ti3Cl8 exhibits a first-order phase transition; the low-temperature phase is characterized by the trimerizations of Ti ions. In this work, we carry out first-principles calculations on the crystal and electronic structure of Na$_2$Ti$_3$Cl$_8$ at the high- and low-temperature phases. The crystal structures, including the lattice constant and the trimerization of Ti ions, are well reproduced by taking account a small Hubbard correction of 1 eV. The calculated total energy landscape reveals a first-order phase transition with the total energy barrier of 80 meV per formula unit. Analysis of the electronic structure indicates a direct metal bonding among Ti in the trimierized low-temperature phase.