Evolutionary search for novel superhard materials: Methodology and applications to forms of carbon and TiO2

Abstract

We have developed a method for prediction of the hardest crystal structures in a given chemical system. It is based on the evolutionary algorithm USPEX (Universal Structure Prediction: Evolutionary Xtallography) and electronegativity-based hardness model that we have augmented with bond-valence model and graph theory. These extensions enable correct description of the hardness of layered, molecular, and low-symmetry crystal structures. Applying this method to C and TiO2, we have (i) obtained a number of low-energy carbon structures with hardness slightly lower than diamond and (ii) proved that TiO2 in any of its possible polymorphs cannot be the hardest oxide, its hardness being below 17 GPa.

Submitted in November 2010; revised in March 2011; resubmitted 24 June 2011; published 12 September 2011. 8 pages, 2 tables, 3 figures

References in corpus (2)

• On the Hardness of a New Boron Phase, Orthorhombic γ-B28
• Ab initio study of the formation of transparent carbon under pressure

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