arXiv subjects

Takehiro Yonehara

Publications and source records attributed to Takehiro Yonehara.

5 recordsLinked to original sources

arXiv2023

Finite temperature effects on the structural stability of Si-doped HfO$_{2}$ using first-principles calculations

The structural stabilities of the monoclinic and tetragonal phases of Si-doped HfO$_{2}$ at finite temperatures were analyzed using a computational scheme to assess the effects of impurity doping. The finite temperature effects considered in this work represented lattice vibration and impurity configuration effects. The results show that 6% Si doping stabilizes the tetragonal phase at room temperature, although a higher concentration of Si is required to stabilize the tetragonal phase at zero temperature. These data indicate that lattice vibration and impurity configuration effects are important factors determining structural stability at finite temperatures.

cond-mat.mtrl-sci↗

arXiv2020

Role of disorder and fluctuation on charge migration dynamics in molecular aggregate with quantum mechanical network

We examine the effect of structural disorder and dynamical lattice fluctuation on charge migration dynamics starting from a birth of local exciton in a quantum network of molecular aggregates by using model Hamiltonians having complicate interactions. Here all monomers are supposed to be the same for simplicity. A natural use of inherent sparsity of Hamiltonian matrix allows us an investigation of essential features in quantum network dynamics accompanied with a fluctuation of interaction. Variation of disorder parameter, kinetic energy and effective mass of monomers in electron dynamics calculation reveal how static disorder and dynamical fluctuation affects electron dynamics in a large size of molecular aggregates. Disorder in aggregate structure suppress charge separation while molecular motion can promote charge diffusion in cases of smaller mass. These findings are obtained by using a newly introduced formula for evaluating charge separation in molecular aggregates that is useful for other analysis involved with charge migration dynamics in molecular/atom aggregates. This work provides a way for obtaining a quantum mechanical time-dependent picture of diffusion and migration of exciton and charge density in general molecular aggregates, which offers a fundamental understanding of electronic functionality of nanocomposites.

physics.chem-ph↗

arXiv2020

Stereo-specific internally entangled roaming mechanism in the reaction of unstable B5 cluster with H

A new type of, called stereo-specific entangled, roaming mechanism is presented in the reaction of structurally unstable B5 cluster with the hydrogen atom, by using the direct ab initio trajectory calculation with a practical level of DFT method using the rang-separated functional. In this mechanism, the light moiety, i.e. H roams around far from the B5 cluster caused by a stereo-specific energy transfer of translational energy to the cluster vibrational energy through the direct coupling due to the large amplitude motion of the unstable B5 cluster. We confirmed by the comparative computation that a clear change occur from the roaming trajectory to the repulsive trajectory, when we froze the vibrational motion of the B5 cluster. This drastic change of the trajectory due to the change between the structurally unstable B5 cluster and the frozen B5 cluster revealed the importance of kinematic energy transfer resulted in the soft-landing-like hydrogen absorption which manifested the present stereo-specific entangled roaming mechanism. The trajectory calculation revealed that the present new type of roaming mechanism is very sensitive to the azimuthal angle of the H atom attack, especially to the bisection of the B-B bond of the B5 cluster, where the energy flow from relative kinetic energy to the vibrational energy of the cluster efficiently takes place through the roaming trajectory driven due to the structural fluctuation of the B5 cluster.

physics.chem-ph↗

arXiv2019

Electron dynamics method using a locally projected group diabatic Fock matrix for molecules and aggregates

We propose a method using reduced size of Hilbert space to describe an electron dynamics in molecule and aggregate based on our previous theoretical scheme [ T. Yonehara and T. Nakajima, J. Chem. Phys. \textbf{147}, 074110 (2017) ]. The real-time time-dependent density functional theory is combined with newly introduced projected group diabatic Fock matrix. First, this projection method is applied to a test donor--acceptor dimer, namely, a naphthalene--tetracyanoethylene with and without initial local excitations and light fields. Secondly, we calculate an absorption spectrum of five-unit-polythiophene monomer. The importance of feedback of instantaneous density to Fock matrix is also clarified. In all cases, half of the orbitals were safely reduced without loss of accuracy in descriptions of properties. The present scheme provides one possible way to investigate and analyze a complex excited electron dynamics in molecular aggregates within a moderate computational cost.

physics.chem-ph↗

arXiv2017

A quantum dynamics method for excited electrons in molecular aggregate system using a group diabatic Fock matrix

We introduce a practical calculation scheme for the description of excited electron dynamics in molecular aggregated systems within a locally group diabatic Fock representation. This scheme makes it easy to analyze the interacting time-dependent excitations of local sites in complex systems. In addition, light-electron couplings are considered. The present scheme is intended for investigations on the migration dynamics of excited electrons in light-energy conversion systems. The scheme was applied to two systems: a naphthalene(NPTL)-tetracyanoethylene(TCNE) dimer and a 20-mer circle of ethylene molecules. Through local group analyses of the dynamical electrons, we obtained an intuitive understanding of the electron transfers between the monomers.

physics.chem-ph↗