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

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. framework of an extension to the linear muffin-tin orbital (LMTO) technique including a highly precise and efficient full-potential implementation. An advanced fully-relativistic, non-collinear implementation based on the atomic sphere approximation is used for calculating transport and magnetic properties.

First-principles study of electronic transport and structural properties of Cu12Sb4S13 in its high-temperature phase

“…This seems like a good approximation for metals where core-hole screening is efficient. Furthermore, a relativistic Full Potential Linear Muffin-Tin Orbital (FP-LMTO) treatment of the magnetic quantum number 19 has been implemented in the QUESTAAL package 20,21 and used to evaluate the core binding energies of the Cu 2p 1/2 and 2p 3/2 electronic states. The smoothed LMTO basis used in this work includes atomic orbitals with l ≤ l max = 4 with orbitals 4d of Sb and Cu added in the form of local orbitals.…”

Evening out the spin and charge parity to increase $${T}_{c}$$ in $${{\rm{Sr}}}_{2}{{\rm{RuO}}}_{4}$$

“…Also, non-local spin, charge, and pairing susceptibilities can also be obtained from vertices computed from the local two-particle Green's sampled by DMFT and bubble diagrams, via the solutions of Bethe-Salpeter equations (BSEs) in respective channels. The full numerical implementation is discussed in Pashov et al 23 and codes are available on the open source electron structure suite Questaal 24 . Our GW implementation is adapted from the original ecalj package 25 .…”

Role of the lattice in the light-induced insulator-to-metal transition in vanadium dioxide

“…In this work, we address the controversy on whether the IMT in VO 2 is purely electronic or is driven by lattice distortions. We use two different routes: ultrafast terahertz (THz) spectroscopy techniques and quasiparticle self-consistent GW theory (QSGW) [28,29]. While the two approaches, in our treatment, are independent, we reach the same conclusion.…”