# Renormalization of the Mott gap by lattice entropy: The case of 1T-TaS2

## TL;DR

This study reveals how lattice entropy influences the Mott gap in 1T-TaS2, showing a continuous gap reduction with temperature increase due to CDW fluctuations, using ab initio molecular dynamics.

## Contribution

It introduces a novel ab initio molecular dynamics approach to quantify lattice entropy effects on the Mott gap in transition-metal dichalcogenides.

## Key findings

- The Mott gap decreases continuously with rising temperature.
- Dynamical CDW fluctuations significantly reduce the Mott gap before phase transition.
- The gap reduction exceeds the effect of lattice temperature variation by an order of magnitude.

## Abstract

In many transition-metal oxides and dichalcogenides, the electronic and lattice degrees of freedom are strongly coupled, giving rise to remarkable phenomena, such as metal-insulator transition (MIT) and charge-density wave (CDW) order. We study this interplay by tracing the instant electronic structure under ab initio molecular dynamics. Applying this method to a 1T-TaS2 layer, we show that the CDW-triggered Mott gap undergoes a continuous reduction as the lattice temperature raises, despite a nearly constant CDW amplitude. Before the CDW order undergoes a sharp first-order transition around the room temperature, the dynamical CDW fluctuation already shrinks the Mott gap size by half. The gap size reduction is one order of magnitude larger than the lattice temperature variation. Our calculation not only provides an important clue to understand the thermodynamics behavior in 1T-TaS2, but also demonstrates a general approach to quantify the lattice entropy effect in MIT.