Kyozaburo Takeda

Electronic structure of chain-like polystannane

Abstract The electronic structure of polystannane (PSn), (SnH 2 ) n , has been calculated by the first principle local density functional method. The effect of bond-angle distortion on PSns first band gap is also investigated theoretically. The common features in the group IV polymers are then summarized by comparison with previous calculated results for polysilane (SiH 2 ) n and polygermane (GeH 2 ) n .

Structure and band models for wide optical gap polysilane alloys

Abstract The microscopic structure and band models have been presented for wide optical-gap polysilane alloys. The experimentally obtained optical properties are explained by the models.

Electrical field manipulation of peptide nanotube at finite temperature (a DFT/MD study)

The effect of applied electric field on a base class of peptide nanotubes (PNT) is simulated using molecular dynamics (MD). A conformational change in the base ring components is found at critical electric field strength, resulting in macroscopic changes to the nanotube (overall length, torque, pore radius, dipole, etc). The effect of temperature, solvent, and computational method is explored.

Time-dependent resonant UHF CI approach for the photo-induced dynamics of the multi-electron system confined in 2D QD

We extend the static multi-reference description (resonant UHF) to the dynamic system in order to include the correlation effect over time, and simplify the TD Schrodinger equation (TD-CI) into a time-developed rate equation where the TD external field Ĥ′(t) is then incorporated directly in the Hamiltonian without any approximations. We apply this TD-CI method to the two-electron ground state of a 2D quantum dot (QD) under photon injection and study the resulting two-electron Rabi oscillation.

Spin-orbit interaction and novel shell structure for multi-electron system confined in 2D QD

By implementing Pauli’s spin-orbit (s/o) coupling and Darwin’s relativistic correction, we study how relativistic terms affect the Schrodinger picture of electrons in a 2D quantum dot (QD). The competition between electron confinement and Pauli’s s/o coupling produces a novel shell structure at Ω0u2009=u20094mc2/ħ, and the inclusion of these relativistic terms is strictly restricted in the Schrodinger picture to ω < Ω0.

Singlet‐Triplet Ground‐State Instability in Square Quantum Dot

We theoretically study the spin multiplicity in the ground state of the square quantum dot (SQD) including four electrons, and discuss a possibility of the singlet‐triplet (S/T) instability in the quantum system. As predicted by Hunds rule, the ground‐state triplet appears when the DQD has a point group symmetry of D4h. This ground‐state triplet is also found even in the deformed SQD (D2h) if the confinement length L is elongated. Consequently, the S/T instability is expected along these boundary lines. It is also worthwhile to notice that the present DFT as well as UHF calculation predicts the spin‐singlet ground‐state when the inter‐electron interaction is strengthened (larger L) even though the SQD maintains its geometrical form of D4h. The strong electron‐localization causes the destabilization in the orbital (kinetic) energies, and produces this characteristic “anti‐Hund” state.

Self‐Induced Oscillation for Electron‐Hole Pair Confined in Quantum Dot

We study the time‐dependent (TD) phenomena of the electron‐hole or electron‐electron pair confined in the square quantum dot (SQD) system by computationally solving TD Schroedinger equation under the unrestricted Hartree‐Fock (UHF) approach. A typical vacillation is found both in the electron and hole when the charged pair is strongly confined in the SQD while the charged particles have initially the same orbital symmetry. The FFT analysis elucidates that the transition matrix element due to the coulomb interaction involves the eigen frequency ω being equal to the excitation energy when the resonative vacillation appears. Thus, Coulomb potential has a potential to cause the self‐induced “Rabi” oscillation when the charged‐particle pair is confined only in the QD.