Structural Instability in Polyacene : A Projector Quantum Monte Carlo Study

TL;DR

This study uses projector quantum Monte Carlo to analyze how electron correlations influence Peierls' instability in polyacene, revealing enhanced instability and specific distortion preferences, with implications for understanding quasi-one-dimensional systems.

Contribution

It provides the first detailed quantum Monte Carlo analysis of electron correlation effects on Peierls' instability in polyacene, highlighting the role of interactions in bond distortion tendencies.

Findings

Electron correlations enhance Peierls' instability in polyacene.

Cis-distortion is favored over trans-distortion.

No evidence of charge density wave formation was found.

Abstract

We have studied polyacene within the Hubbard model to explore the effect of electron correlations on the Peierls' instability in a system marginally away from one-dimension. We employ the projector quantum Monte Carlo method to obtain ground state estimates of the energy and various correlation functions. We find strong similarities between polyacene and polyacetylene which can be rationalized from the real-space valence-bond arguments of Mazumdar and Dixit. Electron correlations tend to enhance the Peierls' instability in polyacene. This enhancement appears to attain a maximum at $U/t \sim 3.0$ and the maximum shifts to larger values when the alternation parameter is increased. The system shows no tendency to destroy the imposed bond-alternation pattern, as evidenced by the bond-bond correlations. The cis- distortion is seen to be favoured over the trans- distortion. The spin-spin correlations show that undistorted polyacene is susceptible to a SDW distortion for large interaction strength. The charge-charge correlations indicate the absence of a CDW distortion for the parameters studied.