New metallic carbon crystal.

Recently, mathematical analysis clarified that sp;{2} hybridized carbon should have a three-dimensional crystal structure (K4) which can be regarded as a twin of the sp;{3} diamond crystal. In this study, various physical properties of the K4 carbon crystal, especially for the electronic properties, were evaluated by first principles calculations. Although the K4 crystal is in a metastable state, a possible pressure induced structural phase transition from graphite to K4 was suggested. Twisted pi states across the Fermi level result in metallic properties in a new carbon crystal.