Dynamical Coherent-Potential Approximation and Tight-Binding Linear Muffintin Orbital Approach to Correlated Electron System

Abstract

Dynamical Coherent-Potential Approximation (CPA) to correlated electrons has been extended to a system with realistic Hamiltonian which consists of the first-principles tight-binding Linear Muffintin Orbital (LMTO) bands and intraatomic Coulomb interactions. Thermodynamic potential and self-consistent equations for Green function are obtained on the basis of the functional integral method and the harmonic approximation which neglects the mode-mode couplings between the dynamical potentials with different frequency. Numerical calculations have been performed for Fe and Ni within the 2nd-order dynamical corrections to the static approximation. The band narrowing of the quasiparticle states and the 6 eV satellite are obtained for Ni at finite temperatures. The theory leads to the Curie-Weiss law for both Fe and Ni. Calculated effective Bohr magneton numbers are 3.0 µB for Fe and 1.2 µB for Ni, explaining the experimental data. But calculated Curie temperatures are 2020 K for Fe and 1260 K for Ni, being still overestimated by a factor of two as compared with the experimental ones. Dynamical effects on electronic and magnetic properties are discussed by comparing with those in the static approximations.

Dynamical coherent-potential approximation approach to excitation spectra in3dtransition metals

“…We consider here a transition metal system with an atom per unit cell, and adopt the TB-LMTO Hamiltonian combined with a LDA+U Coulomb interactions as follows 21 .…”

“…H 0 (τ ) (H 1 (τ )) is the interaction representation of Hamiltonian H 0 (H 1 ). We transform the interaction H 1 (τ ) in the free energy into a one-body dynamical potential v making use of the Hubbard-Stratonovich transformation 12,21 . The transformation is a Gaussian formula for the Bose-type operator {b µ }.…”

“…Here (H 0 ) iLσjL ′ σ is the one-electron Hamiltonian matrix for the noninteracting Hamiltonian H 0 , and (15) has been obtained within the harmonic approximation 20,21,37,38 . It is based on an expansion of E dyn (ξ) with respect to the frequency mode of the dynamical potential v Lσσ ′ (iω ν ), where ω ν = 2νπ/β.…”

“…Their first few terms are given in Appendix A of our paper II 21 . Approximate expressions for higher-order terms will be given in the next section.…”

“…In the next paper 20 which we refer to I in the following, we developed an analytic method to the dynamical CPA, using the harmonic approximation. In the recent paper 21 which we refer to II, we proposed the first-principles dynamical CPA which combines the dynamical CPA with the tight-binding linear-muffintin-orbital (TB-LMTO) 22 base LDA+U Hamiltonian 23 . Within the 2nd-order dynamical corrections to the static approximation, we have shown that the dynamical CPA can describe the finite temperature properties of excitations and magnetism in Fe and Ni quantitatively or semiquantitatively.…”