Phase diagram of tetragonal manganites

The phase diagram of La1-xSrxMnO3, as a function of hole doping x and tetragonal distortion c/a, which consists of ferromagnetic (FM), A-, C-, and G-type antiferromagnetic (AF) states, is obtained by the first-principles band structure calculations. Effects of tetragonal distortion on the magnetic ordering are discussed in terms of orbital ordering and anisotropy in the hopping integrals. The general sequence of the magnetic ground states, FM --> A-AF --> C-AF --> G-AF with increasing of x, is also explained based on the instability of FM states with respect to the spin-wave excitations.

Atomic and electronic origins of a type- C defect on Si(001)

We present an extensive set of ab initio calculations for a type- C defect on Si(001). Various models belonging to subsurface defects are studied. A substitutional B in the second surface layer is predicted as a possible atomic origin of this defect. However, H and O coupled with second-layer vacancies and a substitutional C are not responsible for a type- C defect. We also discuss how the electronic structure of a type- C defect contributes to its specific scanning tunneling microscopy images.

Ab initio simulation of phase transitions and dissociation of H2S at high pressure

By ab initio constant pressure molecular dynamics, we have identified the structure of phase V and phase VI of H2S at 35 and 65 GPa, respectively. The theoretical IR spectra of both phases are consistent with experimental findings and support our proposed structural models. We find that phase V is characterized by the presence of charged SH+3 and SH- species which are created and destroyed dynamically, whereas phase VI is no longer a molecular phase but consists of sheets of S with the majority of H intercalated between the layers. The stability of the two phases with respect to dissociation into elemental crystalline hydrogen and sulfur is discussed.