$i$QIST v0.7: An open source continuous-time quantum Monte Carlo impurity solver toolkit

TL;DR

The paper introduces iQIST v0.7, an improved open-source toolkit for solving quantum impurity models using continuous-time quantum Monte Carlo methods, with enhanced architecture, new observables, and optimized performance.

Contribution

It presents a complete redesign of iQIST, incorporating new basis representations, additional physical observables, and optimized measurement techniques to improve efficiency and capabilities.

Findings

Enhanced computational efficiency and speed.

Added new physical observables like charge susceptibility and fidelity susceptibility.

Supported both particle-hole and particle-particle channels.

Abstract

In this paper, we present a new version of the $i$QIST software package, which is capable of solving various quantum impurity models by using the hybridization expansion (or strong coupling expansion) continuous-time quantum Monte Carlo algorithm. In the revised version, the software architecture is completely redesigned. New basis (intermediate representation or singular value decomposition representation) for the single-particle and two-particle Green's functions is introduced. A lot of useful physical observables are added, such as the charge susceptibility, fidelity susceptibility, Binder cumulant, and autocorrelation time. Especially, we optimize measurement for the two-particle Green's functions. Both the particle-hole and particle-particle channels are supported. In addition, the block structure of the two-particle Green's functions is exploited to accelerate the calculation. Finally, we fix some known bugs and limitations. The computational efficiency of the code is greatly enhanced.