Short-range ordering effects on the electronic Bloch spectral function of real materials in the nonlocal coherent-potential approximation

Abstract

The nonlocal coherent-potential approximation provides a systematic technique for the study of short-range ordering effects in a variety of disordered systems. In its original formulation the technique, however, shows an unwanted dependence on details in the coarse-grained effective medium construction. This is particularly evident in the study of k-resolved quantities, such as the Bloch spectral function and other non-site-diagonal observables. We remove the issue and recover fully physical results in first principles studies of real materials, by means of a resampling procedure first proposed for model tight-binding Hamiltonians. The prescription is further generalized to the case of complex unit cell compounds, with more than a single sublattice, and illustrated through examples from metallic alloys and disordered local moment simulations of paramagnetism in the prototype iron-based superconductor FeSe.

Ab initio calculation of the magnetic Gibbs free energy of materials using magnetically constrained supercells

“…( 9)] can be naturally extended beyond the simplest single-site Weiss field parameters [21]. In other words, magnetically constrained supercell calculations can be directly used to account for nonlocal magnetic correlations akin to the nonlocal coherent po-tential approximation [64,65,81]. Along these lines, spin-cluster expansions, which also follow an adiabatic approximation for the local moments, can be used to efficiently construct complex magnetic Hamiltonians [82].…”

“…The magnetic disorder characterizing the highly fluctuating paramagnetic state (m = 0) covers a wide range of magnetic excitations, which directly impacts the underlying electronic structure. Disorder typically broadens the spectral density function of electronic states in perfect periodic metals [63][64][65]. Consequently, a broadening of the total density of states (DOS) is also expected, as shown in Fig.…”

An averaged cluster approach to including chemical short range order in KKR-CPA

“…Marmodoro et al 18 improved NL-CPA, making it applicable to multiple sublattices and complex geometries (MSNLCPA). Further improvements to the approach were proposed and applied to iron-based superconductor FeSe 19 . While NL-CPA has several desirable features, it is difficult to apply to systems that have a very large configuration space.…”