Complex low energy tetrahedral polymorphs of group IV elements from first-principles

TL;DR

This study uses advanced computational methods to discover three new low-energy, stable carbon polymorphs with unique structures and electronic properties, including the widest band gap among carbon allotropes, with potential applications in semiconductors.

Contribution

It introduces a combined stochastic search strategy to identify novel low-energy carbon structures with unique topologies and properties, expanding the known carbon allotrope landscape.

Findings

Discovered three new stable carbon polymorphs with unique topologies.

Identified a carbon allotrope with the widest band gap of 7.25 eV.

Showed these structures are also stable for silicon, germanium, and tin.

Abstract

The energy landscape of carbon is exceedingly complex, hosting diverse and important metastable phases, including diamond, fullerenes, nanotubes and graphene. Searching for structures, especially those with large unit cells, in this landscape is challenging. Here we use a combined stochastic search strategy employing two algorithms (AIRSS and RG2) to apply connectivity constraints to unit cells containing up to 100 carbon atoms. We uncover three low energy carbon polymorphs (Pbam-32, P6/mmm and I-43d) with new topologies, containing 32, 36 and 94 atoms in their primitive cells, respectively. Their energies relative to diamond are 96 meV/atom, 131 meV/atom and 112 meV/atom, respectively, which suggests potential metastability. These three carbon allotropes are mechanically and dynamically stable, insulating carbon crystals with superhard mechanical properties. The I43d structure possesses a direct band gap of 7.25 eV, which is the widest gap in the carbon allotrope family. Silicon, germanium and tin versions of Pbam-32, P6/mmm and I-43d also show energetic, dynamical and mechanical stability. The computed electronic properties show that they are potential materials for semiconductor and photovoltaic applications.