First-principles prediction of a new metallic carbon hydride: bcc-CH$_{2}$

The observation of a new carbon phase in nanoparticles having the body-centered-cubic structure (bcc) has been reported very recently. However, has been suggested that hydrogen is present in the samples forming solid CH$_{2}$ with the anti-cuprite structure. The structural and electronic properties of bcc-C and bcc-CH$_{2}$ are unknown. In the present work we have studied the elastic stability and the electronic structure of these systems by means of first-principles total-energy calculations. The results were obtained with the pseudopotentials LCAO method (SIESTA code) and the Generalized Gradient Approximation (GGA) for the exchange-correlation potential. We have evaluated the structural stability via the elastic properties, we find that bcc-CH$_{2}$ is stable with a lattice parameter very close to the experimental value. In addition, we find that the electronic structure of bcc-CH$_{2}$ exhibits metallic behavior with a relatively high density of states at the Fermi level. The relevance of this new hydride to the problem of hydrogen storage is discussed.