# Questaal: a package of electronic structure methods based on the linear muffin-tin orbital technique

## TL;DR

Questaal is an open-source software suite implementing advanced electronic structure methods based on the linear muffin-tin orbital technique, supporting various theories like DFT, GW, and DMFT for accurate material property calculations.

## Contribution

It introduces a comprehensive, open-source implementation of the LMTO method with new basis functions for full-potential calculations, integrating multiple theoretical approaches.

## Key findings

- Efficient and precise solutions for band structures across different theories.
- Implementation of short-ranged tight-binding basis functions for full-potential calculations.
- Support for multiple levels of theory including DFT, GW, and DMFT.

## Abstract

This paper summarises the theory and functionality behind Questaal, an open-source suite of codes for calculating the electronic structure and related properties of materials from first principles. The formalism of the linearised muffin-tin orbital (LMTO) method is revisited in detail and developed further by the introduction of short-ranged tight-binding basis functions for full-potential calculations. The LMTO method is presented in both Green's function and wave function formulations for bulk and layered systems. The suite's full-potential LMTO code uses a sophisticated basis and augmentation method that allows an efficient and precise solution to the band problem at different levels of theory, most importantly density functional theory, LDA+U, quasi-particle self-consistent GW and combinations of these with dynamical mean field theory. This paper details the technical and theoretical bases of these methods, their implementation in Questaal, and provides an overview of the code's design and capabilities.