Electronic Structure Calculation by First Principles for Strongly Correlated Electron Systems

Abstract

Recent trends of ab initio studies and progress in methodologies for electronic structure calculations of strongly correlated electron systems are discussed. The interest for developing efficient methods is motivated by recent discoveries and characterizations of strongly correlated electron materials and by requirements for understanding mechanisms of intriguing phenomena beyond a single-particle picture. A three-stage scheme is developed as renormalized multi-scale solvers (RMS) utilizing the hierarchical electronic structure in the energy space. It provides us with an ab initio downfolding of the global band structure into low-energy effective models followed by low-energy solvers for the models. The RMS method is illustrated with examples of several materials. In particular, we overview cases such as dynamics of semiconductors, transition metals and their compounds including iron-based superconductors and perovskite oxides, and organic conductors of -ET type.

Muon spin relaxation and neutron scattering investigations of the noncentrosymmetric heavy-fermion antiferromagnet CeRhGe3

“…[1][2][3][4] One of the most attractive and elusive phenomena of these HF systems is the coexistence of magnetism and superconductivity (SC), which is at the forefront of condensed matter research. The SC in HF systems cannot be explained by the BardeenCooper-Schrieffer (BCS) theory relevant for conventional s-wave phonon-mediated superconductors.…”

“…The pairing mechanism in heavy-fermion superconductors (HFSC) is not yet understood, as is also the case in the high T c cuprates (HTSC) and the newly discovered Fe-based superconductors. 3,4 One of the current hypotheses for these unconventional superconductors is that the superconducting pairing is mediated by magnetic interactions, the so-called "magnetic glue." 3,5 Despite large volumes of data available in the literature on HTSC and HFSC, the origin of the SC and pairing mechanism in these classes of materials remains difficult to understand.…”

Coulomb Correlations Intertwined with Spin and Orbital Excitations in LaCoO3

“…The effective Coulomb interaction for t 2g electrons was shown to be significantly reduced due to efficient e g electron screening, providing an improved understanding of LaMO 3 (M = 3d transition metals from Ti to Cu) series of perovskite oxides. This concept of the screened on-site Coulomb interaction has been developed recently using the constrained random-phase-approximation technique [16][17][18].In this Letter, we exploited resonant inelastic X-ray scattering (RIXS) to investigate spin-orbital excitations in LaCoO 3 and to measure its spin-state populations and the renormalized crystal-field excitations across the spinstate transition. an ideal candidate to examine the role of orbital selective screening of Coulomb interactions as a function of temperature.…”

Ab initio derivation of multi-orbital extended Hubbard model for molecular crystals

“…5,13 The inter-molecular screening effects have also been analyzed by several approaches. [5][6][7][8]10 Multi-molecular-orbital properties have attracted recent attention in the single-component molecular solids, [14][15][16] such as [Ni(tmdt) 2 ] and [Au(tmdt) 2 ]. Among these singlecomponent molecular solids, the metallic behavior was first confirmed in [Ni(tmdt) 2 ].…”