Quantum Monte Carlo Impurity Solver for Cluster DMFT and Electronic Structure Calculations in Adjustable Base

TL;DR

This paper introduces a generalized quantum Monte Carlo impurity solver for cluster DMFT that enables high-precision electronic structure calculations, capturing complex multiplet effects and applied to models like Hubbard, t-J, and real materials such as Cerium.

Contribution

The authors extend a diagrammatic quantum Monte Carlo impurity solver to clusters and realistic atomic multiplet structures, enhancing the accuracy of DMFT-based electronic structure calculations.

Findings

Maximal superconducting T_c coincides with maximum scattering rate.

The method accurately captures multiplet effects in valence histograms.

Applied to Hubbard, t-J models, and Cerium, demonstrating broad applicability.

Abstract

We generalized the recently introduced new impurity solver based on the diagrammatic expansion around the atomic limit and Quantum Monte Carlo summation of the diagrams. We present generalization to the cluster of impurities, which is at the heart of the cluster Dynamical Mean-Field methods, and to realistic multiplet structure of a correlated atom, which will allow a high precision study of actinide and lanthanide based compounds with the combination of the Dynamical Mean-Field theory and band structure methods. The approach is applied to both, the two dimensional Hubbard and t-J model within Cellular Dynamical Mean Field method. The efficient implementation of the new algorithm, which we describe in detail, allows us to study coherence of the system at low temperature from the underdoped to overdoped regime. We show that the point of maximal superconducting transition temperature coincides with the point of maximum scattering rate although this optimal doped point appears at different electron densities in the two models. The power of the method is further demonstrated on the example of the Kondo volume collapse transition in Cerium. The valence histogram of the DMFT solution is presented showing the importance of the multiplet splitting of the atomic states.