Local self-energies for V and Pd emergent from a nonlocal LDA+FLEX implementation

• Published in: Physical review. B 2018-04, Vol.97 (15), Article 155128
• Main Authors: Savrasov, Sergey Y., Resta, Giacomo, Wan, Xiangang
• Format: Article
• Language: English
• Subjects: Approximation; Correlation analysis; Density functional theory; Hilbert space; Ladder diagrams; Mathematical analysis; Mean field theory; Variation
• ISSN: 2469-9950; 2469-9969
• DOI: 10.1103/PhysRevB.97.155128

In the spirit of recently developed LDA+U and LDA+DMFT methods, we implement a combination of density functional theory in its local density approximation (LDA) with a k- and ω-dependent self-energy found from diagrammatic fluctuational exchange (FLEX) approximation. The active Hilbert space here is described by the correlated subset of electrons which allows one to tremendously reduce the sizes of the matrices needed to represent charge and spin susceptibilities. The method is perturbative in nature but accounts for both bubble and ladder diagrams and accumulates the physics of momentum-resolved spin fluctuations missing in such popular approach as GW. As an application, we study correlation effects on band structures in V and Pd. The d-electron self-energies emergent from this calculation are found to be remarkably k independent. However, when we compare our calculated electronic mass enhancements against LDA+DMFT, we find that for the longstanding problem of spin fluctuations in Pd, LDA+FLEX delivers a better agreement with experiment, although this conclusion depends on a particular value of the Hubbard U used in the simulation. We also discuss outcomes of a recently proposed combination of k-dependent FLEX with dynamical mean-field theory (DMFT).