QE-CONVERSE: An open-source package for the quantum ESPRESSO distribution to compute non-perturbatively orbital magnetization from first principles, including NMR chemical shifts and EPR parameters

Orbital magnetization, a key property arising from the orbital motion of electrons, plays a crucial role in determining the magnetic behavior of molecules and solids. Despite its straightforward calculation in finite systems, the computation in periodic systems poses challenges due to the ill-defined position operator and surface current contributions. The modern theory of orbital magnetization, formulated in the Wannier representation and implemented within the Density Functional Theory (DFT) framework, offers an accurate solution through the “converse approach.” In this paper, we introduce

, a refactored and modular implementation of the converse method, designed to replace the outdated routines from Quantum ESPRESSO (version 3.2).

integrates recent advancements in computational libraries, including scaLAPACK and ELPA, to enhance scalability and computational efficiency, particularly for large supercell calculations. While

incorporates these improvements for scalability, the main focus of this work is provide the community with a performing and accurate first principles orbital magnetization package to compute properties such as Electron Paramagnetic Resonance (EPR) g-tensors and Nuclear Magnetic Resonance (NMR) chemical shifts, specially in systems where perturbative methods fail. We demonstrate the effectiveness of

through several benchmark cases, including the NMR chemical shift of ²⁷Al in alumina and ¹⁷O and ²⁹Si in α-quartz, as well as the EPR g-tensor of ${}^n\Sigma (n\ge 2)$ radicals and substitutional nitrogen defects in silicon. In all cases, the results show excellent agreement with theoretical and experimental data, with significant improvements in accuracy for EPR calculations over the linear response approach. The

package, fully compatible with the latest Quantum ESPRESSO versions, opens new possibilities for studying complex materials with enhanced precision.

Program summary

Program Title: qe-converse

CPC Library link to program files: https://doi.org/10.17632/3tyhmxknfc.1

Developer's repository link: https://github.com/mammasmias/QE-CONVERSE.git

Licensing provisions: GNU General Public Licence 3.0

Programming language: Fortran 90

Nature of problem: Ab-initio calculation of the EPR g-tensor and the NMR chemical shift in solid state.

Solution method: Compute the orbital magnetization through a non-pertubative method.