As the Si counterpart of graphene, silicene may be defined as an at least partially sp2-hybridized, atom-thick honeycomb layer of Si that possesses π-electronic bands. Here we show that two-dimensional, epitaxial silicene forms through surface segregation on zirconium diboride thin films grown on Si wafers. A particular buckling of silicene induced by the epitaxial relationship with the diboride surface leads to a direct π-electronic band gap at the Γ point. These results demonstrate that the buckling and thus the electronic properties of silicene are modified by epitaxial strain.

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The widespread popularity of density functional theory has given rise to an extensive range of dedicated codes for predicting molecular and crystalline properties. However, each code implements the formalism in a different way, raising questions about the reproducibility of such predictions. We report the results of a community-wide effort that compared 15 solid-state codes, using 40 different potentials or basis set types, to assess the quality of the Perdew-Burke-Ernzerhof equations of state for 71 elemental crystals. We conclude that predictions from recent codes and pseudopotentials agree very well, with pairwise differences that are comparable to those between different high-precision experiments. Older methods, however, have less precise agreement. Our benchmark provides a framework for users and developers to document the precision of new applications and methodological improvements

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We present a microscopic model for the anisotropic exchange interactions in Sr 2 IrO 4 . A direct construction of Wannier functions from first-principles calculations proves the j eff =1/ 2 character of the spin-orbit integrated states at the Fermi level. An effective j eff -spin Hamiltonian explains the observed weak ferromagnetism and anisotropy of antiferromagnetically ordered magnetic state, which arise naturally from the j eff =1/ 2 state with a rotation of IrO 6 octahedra. It is suggested that Sr 2 IrO 4 is a unique class of materials with effective exchange interactions in the spin-orbital Hilbert space.

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We report an implementation of the LDA+ U method based on the state-of-the-art linear combination of pseudo-atomic orbital ͑LCPAO͒ method, which is suitable for large-scale O͑N͒ electronic structure calculations based on the density functional theory. By introducing a dual representation of the occupation number matrix instead of the on-site or full representations, the LDA+ U formalism is refined to be consistent with a nonorthogonal LCPAO basis in regard to the sum rule of the total number of electrons. For typical transition metal oxide bulk systems, the band gap, magnetic moment, and detailed electronic structures are investigated with the different choices of basis orbitals and effective U values as well as the definition of the occupation number matrix. The results are in good agreement with previous theoretical and experimental studies, indicating that the proposed LDA+ U scheme combined with the O͑N͒ method is a quite promising approach for the study of large-scale correlated material systems consisting of localized electrons. We discuss the electronic structure and magnetic properties of ͑NiO͒ m / ͑CoO͒ n superlattices as an application of our method.