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We have calculated the phonon dispersion and the electron-phonon interaction in palladium at ambient and under pressure using ab initio methods and evaluated superconducting transition temperature on the basis of the BCS theory. At ambient pressure, we have evaluated the electron-phonon coupling constant to be λ=0.377 by the use of the density-functional perturbation theory, and estimated the spin fluctuation effect in relation to the experimental data of specific heat. The vanishing of the superconducting transition at ambient pressure is resulted from the spin fluctuation effect. The spin fluctuation effect reduces with increasing pressure, and the superconductivity appears under pressure.

We explore the unknown structure of phosphorus in phase IV (P-IV phase) based on first-principles calculations using the metadynamics simulation method. Starting from the simple cubic structure, we find a new modulated structure of the monoclinic lattice. The modulation is crucial to the stability of the structure. Through refining the structure further by changing the modulation period, we find the structure whose x-ray powder diffraction pattern is in best agreement with the experimental pattern. We expect that the modulation period of the structure in the P-IV phase is very close to that found in this study and probably incommensurate.

We searched for the structure of calcium in phases IV and V by a metadynamics simulation based on ab initio calculations, and found two structures. One is a tetragonal lattice which consists of two helical chains along the c axis. The other is an orthorhombic lattice of four zigzag chains. We have calculated the x-ray diffraction patterns and enthalpies of the two structures discovered by our simulation. From comparisons of the patterns with the experimental x-ray patterns of the phases IV and V and from the pressure dependence of the enthalpies, we conclude that the structure with a helical pattern corresponds to phase IV and the structure with a zigzag pattern to phase V.

By applying the recursion method to the intermetallic mixed compound Mn₄N₁₋xCx with cubic perovskite-type structure we investigate the effects of substitution of C atoms for N atoms on the electronic structure and the magnetic properties of Mn₄N. By calculating the DOS's for the ferrimagnetic states of both Mn₄N and Mn₄N₀.₇₅C₀.₂₅ we have determined the magnetic moments at two types of Mn site, Mn(I)(corner site) and Mn(II) (face center site), which are antiparallel to each other. The obtained magnetic moment of Mn(I) in Mn₄N₀.₇₅C₀.₂₅ is found to be the same with that in Mn₄N while the absolute value of Mn(II) moment increases by the substitution of C atoms. As the result the total ferromagnetic moment decreases by the substitution of C atoms. These results are in good agreement with the observations.

We searched for the structure of calcium in phases IV and V by a metadynamics simulation based on ab initio calculations, and found two structures. One is a tetragonal lattice which consists of two helical chains along the c axis. The other is an orthorhombic lattice of four zigzag chains. We have calculated the x-ray diffraction patterns and enthalpies of the two structures discovered by our simulation. From comparisons of the patterns with the experimental x-ray patterns of the phases IV and V and from the pressure dependence of the enthalpies, we conclude that the structure with a helical pattern corresponds to phase IV and the structure with a zigzag pattern to phase V.

The purpose of this lecture is to present basic knowledge to understand various properties and interesting phenomena found in materials. We will introduce important viewpoints in both physics and chemistry based on the quantum mechanics. Theoretical methods in the condensed matter physics enable us to perform not only analysis of known substances in extreme conditions including high pressures and high temperatures but also design of new materials., 大阪大学OpenCourseWare:大学院講義 (留学生向け特別プログラムから)

We explore the unknown structure of phosphorus in phase IV (P-IV phase) based on first-principles calculations using the metadynamics simulation method. Starting from the simple cubic structure, we find a new modulated structure of the monoclinic lattice. The modulation is crucial to the stability of the structure. Through refining the structure further by changing the modulation period, we find the structure whose x-ray powder diffraction pattern is in best agreement with the experimental pattern. We expect that the modulation period of the structure in the P-IV phase is very close to that found in this study and probably incommensurate.