First principles study of a new large-gap nanoporous silicon crystal: Hex-Si-40

We present an ab initio calculation of the structural and electronic properties of Si in a novel hexagonal, fourfold coordinated structure with 40 atoms per unit cell, obtained from the coalescence of small fullerenic cages. Hex-Si-40 has a tubular structure, inducing confined electronic states near the gap, which is widened by similar to 0.4 eV with respect to normal silicon. This system is predicted to be a very interesting, possibly photoluminescent material for optoelectronics.