Orbital Peierls mechanism of the formation of molecular clusters in Na2Ti3Cl8 and in similar systems

TL;DR

This paper explains the formation of molecular clusters in Na2Ti3Cl8 and similar systems through an orbital-driven Peierls transition, simplifying previous complex magnetic explanations.

Contribution

It introduces a straightforward orbital Peierls mechanism as the cause of cluster formation, challenging prior magnetic-based theories.

Findings

Orbital Peierls transition explains cluster formation.

Simplifies understanding of structural transition in Na2Ti3Cl8.

Applicable to similar systems with breathing kagome lattices.

Abstract

Recently the structural transition in Na2Ti3Cl8 at 200 K with the formation of triangular Ti3 clusters was studied by ab-initio calculations in PRL 124, 167203 (2020). It was concluded on the basis of the DFT+U results that the usual band effects are not sufficient to explain this transition. The authors then invoked magnetic mechanisms, including complicated factors such as biquadratic and ring exchanges. We point out that this overcomplicated description is unnecessary, and that the formation of trimers, or breathing kagome lattice in Na2Ti3Cl8, and in many other systems, has very simple, almost trivial explanation basing on the orbital-driven Peierls transition.