Ab initio search for low-enthalpy sp3 carbon using evolutionary metadynamics

Details Ab initio search for low-enthalpy sp3 carbon using evolutionary metadynamics Ab initio search for low-enthalpy sp3 carbon using evolutionary metadynamics

2012-03-04

arxiv.org/abs/1203.0706v3

Physics

Condensed Matter

Materials Science

5 pages, 7 figures

Scientific paper

We present a systematic search for low-energy metastable superhard carbon allotropes by using the recently developed evolutionary metadynamics technique. It is known that cold compression of graphite produces a new allotrope at 15-20 GPa. Here we look for all low-enthalpy structures accessible from graphite. Starting from 2H- or 3R-graphite and applying the pressure of 20 GPa, a large variety of intermediate $sp^3$ carbon allotropes were observed in evolutionary metadynamics simulation. Our calculation not only found all the previous proposed candidates for `superhard graphite', but also predicted two new allotropes (\emph{X}-carbon and \emph{Y}-carbon) showing novel `5+7' and `4+8' topologies. These superhard carbon allotropes can be classified into five families based on `6' (diamond/lonsdaleite), `5+7' (\emph{M/W}-carbon), `5+7' (\emph{X}-carbon), `4+8' (bct C$_4$), and `4+8' (\emph{Y}-carbon) topologies. This study shows evolutionary metadynamics is a powerful approach to systematically search for low-energy metastable phases reachable from given starting materials.

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