Quantum confinement and quasiparticle corrections in α-HgS from first principles

Using a combination of density functional theory and many-body GW corrections, we calculate the quasipartide band gap of bulk alpha-HgS and investigate the effect of quantum confinement on the geometric, electronic and optical structures. The basic structural unit of alpha-HgS is a one-dimensional helical chain consisting of covalently bound Hg and S atoms. When isolated to just a single helix or to a few-helix configuration, we find that alpha-HgS becomes a wide-gap semiconductor with a quasiparticle band gap as large as 7.0 eV, in contrast to the bulk structure with a direct quasiparticle band gap of 2.8 eV and an indirect gap of 2.14 eV. This dramatic increase in the band gap is attributed to quantum confinement effects on the geometry and intra-helix bonding. Shifts in the band gaps are also reflected as shifts in the low-energy optical absorption spectra calculated via density functional theory. As more helical chains are added, the band gap decreases sharply while the geometry becomes more bulk-like. This work illustrates the strong effects of quantum confinement in low-dimensional a-HgS nanostructures. (C) 2015 Elsevier B.V. All rights reserved.