Tuning of the CDW in the Halogen-Bridged Transition-Metal Linear-Chain Compounds

TL;DR

This paper uses calculations to show how metal-metal distance influences the charge-density wave in halogen-bridged transition-metal chains, predicting a phase transition and explaining various physical trends.

Contribution

It introduces a model incorporating ion-ion repulsion to explain the CDW behavior and predicts a phase transition in these compounds.

Findings

Metal-metal distance controls CDW strength

Predicted second-order phase transition from insulator to semi-metal

Explained trends in dimerization, bond ratios, band gaps, and Raman modes

Abstract

Local-density-approximation calculations are used to show that the metal-metal distance along the chains controls the charge-density wave (CDW) in halogen-bridged transition-metal linear-chain (MX) compounds. The strength of the CDW can be understood in terms of a two band Su-Schrieffer-Heeger model if a hard-core ion-ion repulsion potential is also added. We predict a second-order phase transition from an insulating to a semi-metallic ground state and explain trends in dimerization, bond-length ratios, band gaps, and Raman breathing modes in terms of the metal-metal distance. Three "ps" figures are included at the end of the file.