2025년 11월 6일(목) 물리학과 콜로퀴움 안내입니다.

연사: 장보규 교수님 (경희대)

시간: 15시~17시

강연장소: 학산도서관 지하 1층 세미나실

강연제목: Nonlocal Coulomb Interaction in mixed-valence compounds

초록: 

The DFT+U+V method is an extension of the DFT+U approach that includes inter-site Coulomb interactions V in addition to on-site Coulomb interaction U. This extension improves the accuracy of the DFT+U method in systems where the hybridization between orbitals at different atomic sites is important. Recently, this new method has received great attention due to its high accuracy in correcting self-interactions and its low computational costs [1]. It has successfully described various properties of solids such as semiconductor band gaps [1], Li-ion battery voltages [2], and perovskites defect states [3].

In this presentation, I will discuss the application of DFT+U+V approach to study mixed valence compounds. Firstly, I will examine the prototypical charge-ordered material BaBiO3, where the charge-ordered state can be suppressed by substituting Ba with K, leading to superconductivity. However, the conventional DFT method fails to describe its physical properties. Our study reveals that the inter-site Coulomb interaction V is essential to describe all their doping-dependent experimental features such as breathing instabilities and electron-phonon matrix element [4]. Secondly, I will discuss LiCu₂O₂ which contains Cu(II) (d⁹) and Cu(I) (d¹⁰) ions in its crystal structure. This material exhibits an unprecedented 250 % broadening of the bandwidth compared to the DFT prediction [5]. However, DFT+U+V successfully describes the experimental bandwidth, indicating the significance of inter-site Coulomb interaction in this system.

[1] S.-H. Lee and Y.-W. Son, Phys. Rev. Res. 2, 043410 (2020).

[2] M. Cococcioni and N. Marzari, Phys. Rev. Mater. 3, 033801 (2019).

[3] C. Ricca, I. Timrov, M. Cococcioni, N. Marzari, and U. Aschauer, Phys. Rev. Res. 2, 023313 (2020).

[4] B. G. Jang, M. Kim, S.-H. Lee, W. Yang, S.-H. Ji, and Y.-W. Son, Phys. Rev. Lett. 130, 136401 (2023).

[5] M. Moser et al., Phys. Rev. Lett. 118, 176404 (2017).

Host: 김정우 교수님