Structure Deformation and Level Splitting in Vacancy-Centered Hexagonal Armchair Nanographene

Abstract

We provide a theoretical proof of the protected degeneracy in zero modes found in a set of molecular structures called the vacancy-centered hexagonal armchair nanographene (VANG). Recently, two of the authors (G.K.S, K.K.), T. Enoki, and I. Maruyama have proposed that the molecular nanographene is an ideal material for hydrogen storage applications. In our proof of the tight-binding description of the π-electron system, we utilize the mirror reflection symmetry preserved in the VANG structure as well as the chiral symmetry. Provided that the symmetric operations are maintained, even if the molecular structure is deformed, curious zero modes, the quasi-localized zero mode and the extending zero mode, are degenerate with each other and create the singlet ground state.