No abstract

Using hybrid density functional theory combined with a semiempirical van der Waals dispersion correction, we have investigated the structural and electronic properties of vacancies and self-interstitials in defective few-layer phosphorene. We find that both a vacancy and a self-interstitial defect are more stable in the outer layer than in the inner layer. The formation energy and transition energy of both a vacancy and a self-interstitial P defect decrease with increasing film thickness, mainly due to the upward shift of the host valence band maximum in reference to the vacuum level. Consequently, both vacancies and self-interstitials could act as shallow acceptors, and this well explains the experimentally observed p-type conductivity in few-layer phosphorene. On the other hand, since these native point defects have moderate formation energies and are stable in negatively charged states, they could also serve as electron compensating centers in n-type few-layer phosphorene.Comment: 10 pages, 12 figure

The embrittling and strengthening effects of hydrogen, boron, and phosphorus on a ⌺5(210) ͓100͔ nickel grain boundary are investigated by means of the full-potential linearized augmented plane-wave method with the generalized-gradient approximation formula. Optimized geometries for both the free surface and grainboundary systems are obtained by atomic-force calculations. The results obtained show that hydrogen and phosphorus are embrittlers and that boron acts as a cohesion enhancer. An analysis of the atomic, electronic, and magnetic structures indicates that atomic size and the bonding behavior of the impurity with the surrounding nickel atoms play important roles in determining its relative embrittling or cohesion enhancing behavior.

Simple structures of MnX binary compounds, namely hexagonal NiAs and zincblende, are studied as a function of the anion (X = Sb, As, P) by means of the all-electron FLAPW method within local spin density and generalized gradient approximations. An accurate analysis of the structural, electronic and magnetic properties reveals that the cubic structure greatly favours the magnetic alignment in these compounds leading to high magnetic moments and nearly half-metallic behaviour for MnSb and MnAs. The effect of the anion chemical species is related to both its size and the possible hybridization with the Mn d states; both contributions are seen to hinder the magnitude of the magnetic moment for small and light anions. Our results are in very good agreement with experiment -where available -and show that the generalized gradient approximation is essential to correctly recover both the equilibrium volume and magnetic moment.PACS numbers 71.20.-b,75.30.-m,75.50.-y Typeset using REVT E X 1