第41回 原研・兵県大合同コロキウム

日時: 平成20年4月24日(木) 16:00〜
Date and time: 24th April (Thu.) 16:00〜
場所: SPring-8, 萌光館
Place: SPring-8, "HOUKOUKAN" seminar room
Title: Ab initio Downfolding Approach: Theory and Several Applications
講演者: 中村和磨 氏 (東京大学理学部)
Speaker: Dr. Kazuma Nakamura (Department of Applied Physics, University of Tokyo)
Abstract:

I will talk about our recent advances on ab initio downfolding method aiming at a deeper understanding for various real materials under effects of many-body correlations. At the heart of downfolding lies utilizing the energy hierarchy of the system: The low-energy hierarchy near the Fermi level (εf=±2∼3eV) determines physics while is affected by the remaining high-energy part of hierarchy. We renormalize the high-energy part into the low-energy part and this renormalization generates an effective low-energy model characterized by renormalized transfers and effective screened Coulomb/exchange interactions. The resulting effective model provides us with a reliable starting point to examine the low-energy physics of the system and can be solved with several solvers considering many-body effects at the highly accurate level. I will present several applications of this theory to optical-absorption problems [1], where we especially analyze whether essence and quantitative aspects of electronic excitation spectra are correctly captured by an effective low-energy model constructed from an ab initio downfolding scheme. The resulting spectra quite well reproduce the experimental results, indicating that our downfolding scheme offers a satisfactory framework of the electronic structure calculation, particularly for the excitations and dynamics as well as for the ground state. In addition, our recent challenge to ab intio derivations of low-energy models of complex materials such as transition-metal oxides and organic-molecular solids will be presented and discussed.

  • [1] K. Nakamura, Y. Yoshimoto, R. Arita, S. Tsuneyuki, and M. Imada, Phys. Rev. B (unpublished); arXiv:0710.4371v1.