Title: A Superconductivity Density Functional Theory Based on LDA+U
Speaker: Dr. Ming-Chun Jiang (RIKEN)
Time: 10:30-11:30, August 3 (Mon.), 2026
Place: NCTS Physics 4F Lecture Hall, Cosmology Hall, NTU

Abstract ^[1]:
Superconducting density functional theory (SCDFT) offers an ab initio framework for evaluating superconducting transition temperatures (Tc) by treating electron-phonon coupling, screened Coulomb interactions, and spin fluctuations on a unified basis. However, in materials with partially localized orbitals, conventional spin-fluctuation kernels may underestimate the role of local orbital correlations. In this work, we extend the spin-fluctuation part of SCDFT by incorporating a Hubbard-type local interaction inspired by LDA+U. The key ingredient is a momentum-dependent Hubbard form factor constructed from localized projector wavefunctions, allowing the local interaction to be represented consistently in the reciprocal-space basis used for the spin susceptibility.
I will discuss the implementation strategy, including the construction of the q-dependent Hubbard vertex, its coupling to the spin-fluctuation kernel, and practical checks based on the Stoner criterion. Applications to transition-metal superconductors V and V₃Si show that the added local interaction can substantially modify the spin-fluctuation contribution and therefore the calculated Tc, even when the underlying band structure changes only weakly. This approach provides a route toward a more orbital-resolved and correlation-aware superconducting density functional theory, while also highlighting the need for careful control of effective Hubbard parameters and magnetic stability.

[1] Ming-Chun Jiang¹, Mitsuaki Kawamura², and Ryotaro Arita^{1,3
      1} Center for Emergent Matter Science, RIKEN, Wako 351-0198, Japan
      ² Division of Intelligent Systems Engineering, Yokohama National University, Yokohama 240-8501, Japan 
      ³ Department of Physics, University of Tokyo, Hongo, Tokyo 113-0033, Japan