Nobuhiko Akino

Optical properties in conjugated polymers

Optical properties in conjugated polymers such as poly(p-phenylenevinylene) and poly(9,9-dialkyl-fluorene) have been studied using time-dependent density functional theory. In the calculations of the optical properties, real-space and real-time techniques are employed. We follow the linear responses of the systems under externally applied perturbations in the real time. To estimate the polymer spectra, we have calculated the responses of oligomers of different lengths and obtained the extrapolated values. The estimated polymer spectra agree with the experiments reasonably well.

56.1: Invited Paper: Excited State Interactions in P-OLEDs: Implications For Efficiency And Lifetime

A fluorescent blue P-OLED has high densities of triplet excited states within the emissive layer. In this paper we will present an efficiency and degradation analysis of model P-OLED devices and materials, and demonstrate that control of triplet transfer and annihilation processes are of crucial importance in realising the efficiencies and device stabilities required for commercialisation of the technology.

Real-time and real-space program tuned in K-computer

We have transported the code from Earth Simulator (ES) to K-Computer (KC) keeping a scalability. The base code achieved remarkable linear scalability and significant parallelization efficiency in EC before. The reason of success is that, taking into account the architectural differences between ES and KC, we improve the program step by step. Actually, the program showed a 37% improvement in the total performance with the implementations such as hybrid OpenMP and MPI parallelization, and the optimal rank mapping, and the MPI communication concealment, including removing the unnecessary processes such as zero clear and data copy.

Optical Responses of Conjugated Polymers by TDDFT in Real-Space and Real-Time Approach

The time dependent density functional theory (TDDFT) has applied to study the optical responses of the conjugated polymers such as poly( p -phenylenevinylene) and poly(9, 9-dialkyl-fluorene). In our study, the real-space grid representation is used for the electron wavefunctions in contrast to a conventional basis set on each atom. In the calculations of the optical responses, the real-time approach is employed, where we follow the linear responses of the systems under externally applied perturbations in the real time. Since a real polymer is too large to handle, we have calculated the oligomers with different length and observed the spectrum peak is redshifted as the length of oligomer increases. The property of the polymer is extrapolated as the infinitely long oligomer. The estimated polymer spectra agree with the experiments reasonably well.

Dielectric Properties of Semiconductors by TDDFT in Real-Space and Real-Time Approach

The dielectric responses of semiconductors such as C, Ge, Si, and AlGaAs are studied by the time-dependent density-functional theory. In our study, the real-space grid representation of the electron wave functions is used and the real-time approach is employed for the dynamics of the system. Both the static and dynamic dielectric functions are calculated, and we yielded that the static dielectric constants e(0) are especially in good agreement with the experimental values. The effect of Al-component in the compound semiconductor Al x Ga 1− x As is also studied. The peaks of the imaginary part of the dielectric function change with the band separation as a function of the Al-component. Furthermore, the static dielectric constants show the expected change due to the band separation as a function of the Al-component.