A multi-orbital iterated perturbation theory for model Hamiltonians and real material-specific calculations of correlated systems

TL;DR

This paper introduces a multi-orbital iterative perturbation theory (MO-IPT) method for studying correlated electron systems, combining it with dynamical mean field theory and density functional theory to analyze model and real materials like SrVO3.

Contribution

The paper develops a novel multi-orbital IPT approach that improves computational efficiency and accuracy for complex correlated systems, including real material calculations.

Findings

MO-IPT shows good agreement with CTQMC away from particle-hole symmetry.

The method effectively models Hund's coupling effects in multi-orbital systems.

Application to SrVO3 demonstrates accurate density of states and photo emission spectra.

Abstract

Perturbative schemes utilizing a spectral moment expansion are well known and extensively used for investigating the physics of model Hamiltonians and real material systems. The advantages they offer, in terms of being computationally inexpensive, with real frequency output at zero and finite temperatures, compensate for their deficiencies and offer a quick, qualitative analysis of the system behavior. In this work, we have developed a method, that can be classified as a multi-orbital iterative perturbation theory (MO-IPT) to study N-fold degenerate and non degenerate Anderson impurity models. As applications of the solver, we have combined the method with dynamical mean field theory to explore lattice models like the single orbital Hubbard model, covalent band insulator and the multi-orbital Hubbard model for density-density type interactions in different parameter regimes. The Hund's coupling effects in case of multiple orbitals is also studied. The limitations and quality of results are gauged through extensive comparison with data from the numerically exact continuous time quantum Monte Carlo method (hybridization expansion CTQMC). In general we observe that the agreement with CTQMC results gets better as we move away from particle-hole symmetry. We have integrated MO-IPT with density functional theory based electronic structure methods to study real material systems. As a test case, we have studied the classic, strongly correlated electronic material, SrVO$_3$. A comparison of density of states and photo emission spectrum (PES) with results obtained from different impurity solvers and experiments yields good agreement.