The interplay of sp2- and sp3-type bonding defines silicon allotropes in two- and three-dimensional forms. A novel two-dimensional phase bearing structural resembleance to a single MoS2 layer is found to possess a lower total energy than low-buckled silicene and to be stable in terms of its phonon dispersion relations. A new set of cigar-shaped, nematic orbitals originating from the Si sp2 orbitals realizes bonding with a 6-fold coordination of the inner Si atoms of the layer. The identification of these nematic orbitals advocates diverse Si bonding configurations different from those of C atoms.
@article{arxiv.1401.0142,
title = {Diverse forms of $\sigma$ bonding in two-dimensional Si allotropes: Nematic orbitals in the $MoS_2$ structure},
author = {Florian Gimbert and Chi-Cheng Lee and Rainer Friedlein and Antoine Fleurence and Yukiko Yamada-Takamura and Taisuke Ozaki},
journal= {arXiv preprint arXiv:1401.0142},
year = {2015}
}