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The electronic and optical properties of hybrid perovskites CH3NH3SnX3 (X = Br, I) are investigated by first-principles calculations. Our results show that consideration of the weak van der Waals interactions is important for theoretical investigations of Sn-based hybrid materials. During light harvesting, the electron transition will occur between the p states of halogen at the valence band maximum (VBM) and the Sn 5p states at the conduction band minimum (CBM). Comparing with the energy distribution of solar spectra, CH3NH3SnI3 has better absorption characteristics in the visible region than CH3NH3PbI3, which shows promising prospects in realizing lead-free, highly efficient solar cells.

Compression properties and deformation modes of closed-cell foam are investigated at different impact velocity. The contrast of deformation modes indicates that both uniform and negative graded foam have quasi-static mode, transitional mode and impact mode. On the contrary, the positive graded foam only has one mode; the local deformation propagates from impact end towards supported end.

We study an inhomogeneous three-orbital Hubbard model for the Cu-substituted iron pnictides using an extended real-space Green's function method combined with density functional calculations. We find that the onsite interactions of the Cu ions are the principal determinant of whether an electron dopant or a hole dopant is caused by the Cu substitution. It is found that the Cu substitution could lead to a hole doping when its onsite interactions are smaller than a critical value, as opposed to an electron doping when the interactions of Cu ions are larger than the critical value, which may explain why the effects of Cu substitution on the carrier density are entirely different in NaFe$_{1-x}$Cu$_x$As and Ba(Fe$_{1-x}$Cu$_x$)$_2$As$_2$. We also find that the effect of a doping-induced disorder is considerable in the Cu-substituted iron pnictides, and its cooperative effect with electron correlations contributes to the orbital-selective insulating phases in NaFe$_{1-x}$Cu$_x$As and Ba(Fe$_{1-x}$Cu$_x$)$_2$As$_2$., Comment: 13 pages, 11 figures

The electronic structures and magnetic properties induced by the substitution of Mg in MgCNi3 were investigated by performing the first-principles density functional calculations. It is confirmed that AlCNi3, GaCNi3, and InCNi3 are paramagnetic nonsuperconductors resulting from total energy, density of states at Fermi level, and electron-phonon coupling constant. A large peak of density of states lies on the Fermi level, resulting in ferromagnetism rather than superconductivity in NaCNi3. The substitution of dual elements for Mg, such as Al0.5Na0.5CNi3 and Al0.5Li0.5CNi3, was inspected too. Evaluating the electron-phonon coupling interaction, the possible superconductivity exists in near ferromagnetic Al0.5Na0.5CNi3.

The effects on the electronic structure and magnetic property of the Ni site substitution in nonoxide perovskite superconductor MgCNi3 are studied by using density functional calculations. A sharp high peak of Ni d density of states just lies below the Fermi energy in pure MgCNi3. Co-doping results in the onset of ferromagnetism at x=0.083. However, the little energy gain as well as small magnetic moment per atom indicate the weak itinerant ferromagnetism. The strong ferromagnetic spin fluctuation in MgCNi3−xCox leads to quench bulk superconductivity, while the Mn atom forms a local magnetic moment of 1.06 μB at x=0.042 which suppresses superconductivity more seriously than Co does in the low doping case. Cu doping can be well accounted for by the rigid band model, which reduces the density of states at the Fermi level and the Tc.