Research

Organic conductors

The BEDT-TTF salts, which have two-dimensional BEDT-TTF and anion layers, have many interesting phsical properties.

beta'-(BEDT-TTF)2X is the Mott insulator at ambient pressure. beta'-(BEDT-TTF)2ICl2 shows superconductivity at pressures, while beta'-(BEDT-TTF)2AuCl2 does not show superconductivity at pressures. They are isostructural materials, but shows other phases. We have clalified the electronic structure at pressures in the first-principles study. Next we studied the phase diagram in the effective model Hamiltonian. The resultant phase diagram shows that beta'-(BEDT-TTF)2ICl2 shows superconductivity, while beta'-(BEDT-TTF)2AuCl2 does not show superconductivity. This originates from the small difference of the warping of the Fermi surfaces.

alpha-(BEDT-TTF)2I3 is an insulator with charge-disproportionation at ambient pressures. It is metallic at pressures. The conductivity is proportional to the T-square at low temperatures in the metallic phase, and has high mobility. Our calculation clarified the existence of the two-dimensional massless-Dirac cone dispersion at the Fermi level.

First-Principles calculation of conductance

tutorial of Non-equilibrium Green function method (pdf or html)
This method is applied to the OpenMX code.
(old) explantions of the code are 1 (pdf) and 2 (pdf).

GW method

GW method takes into account of the RPA correlation in the first-principles calculation.
fullpotentail GWsc result of La0.7Sr0.3MnO3, which is known as a candidate of capacitance of RRAM and MRAM.
-> explanation (pdf) (a work with Dr. Kotani.)

LSDA dispersion of La0.7Sr0.3MnO3

fullpotential self-consistent GWsc dispersion of La0.7Sr0.3MnO3

GW tetrahedron DOS (pdf) in Japanese - tetrahedron DOS with imaginary part of self-energy. The result is also written in the pdf above. (also see the Tools part.)

Quantum Monte-Calro

diffusion Monte-Calro, curve fit with the concept of Baysian statistics.

Possible mechenism of carrier doping into DNA

DNA can be a semiconductor like conducting polymers.
The hydrated divalent cation has the unoccupied state, while the anhydrous one has the occupied state. red: occupied state, blue: unoccupied state.

Software

OpenMX

Dr. T. Ozaki's order(N) program to calculate electronic structure with the local basis set. You can make local basis sets and pseudopotentials easily.
-> link to Dr. Ozaki's web page