Approximative treatment of 5f-systems with partial localization due to intra-atomic correlations

TL;DR

This paper investigates the partial localization of 5f electrons in actinide compounds, comparing various approximation methods to exact solutions to understand their effectiveness in modeling intra-atomic correlations.

Contribution

It provides a microscopic analysis of partial localization using small clusters, highlighting the effectiveness of Gutzwiller and LDA+U approximations over Hartree Fock.

Findings

Gutzwiller and LDA+U approximations describe partial localization well.

Hartree Fock approximation poorly matches exact results.

Hund's rule correlations enhance hopping anisotropy across methods.

Abstract

Increasing experimental and theoretical evidence points towards a dual nature of the 5$f$ electrons in actinide-based strongly correlated metallic compounds, with some 5$f$ electrons being localized and others delocalized. In a recent paper (PRB xxx, 2004), we suggested the interplay of intra-atomic correlations as described by Hund's rules and a weakly anisotropic hopping (hybridization) as a possible mechanism. The purpose of the present work is to provide a first step towards a microscopic description of partial localization in solids by analyzing how well various approximation schemes perform when applied to small clusters. It is found that many aspects of partial localization are described appropriately both by a variational wavefunction of Gutzwiller type and by a treatment which keeps only those interactions which are present in LDA+U calculations. In contrast, the energies and phase diagram calculated within the Hartree Fock approximation show little resemblence with the exact results. Enhancement of hopping anisotropy by Hund's rule correlations are found in all approximations.