Quasiparticle and excitonic gaps of one-dimensional carbon chains

TL;DR

This study uses diffusion quantum Monte Carlo to accurately calculate the electronic and vibrational properties of hydrogen-terminated carbon chains, revealing their sensitivity to atomic structure and providing benchmark data.

Contribution

The paper presents the first DMC calculations of quasiparticle and excitonic gaps of hydrogen-terminated carbon chains, including geometry optimization and phonon frequency estimation.

Findings

Bond-length alternation of polyyne is 0.136 Å.

Excitonic gap is 3.30 eV.

Quasiparticle gap is 3.4 eV.

Abstract

We report diffusion quantum Monte Carlo (DMC) calculations of the quasiparticle and excitonic gaps of hydrogen-terminated oligoynes and polyyne. The electronic gaps are found to be very sensitive to the atomic structure in these systems. We have therefore optimised the geometry of polyyne by directly minimising the DMC energy with respect to the lattice constant and the Peierls-induced carbon-carbon bond-length alternation. We find the bond-length alternation of polyyne to be 0.136(2) {\AA} and the excitonic and quasiparticle gaps to be 3.30(7) and 3.4(1) eV, respectively. The DMC zone-centre longitudinal optical phonon frequency of polyyne is 2084(5) cm$^{-1}$, which is consistent with Raman spectroscopic measurements for large oligoynes.