Band unfolding with a general transformation matrix: from code implementation to interpretation of photoemission spectra

TL;DR

This paper introduces an extended computational tool for band structure unfolding using arbitrary transformation matrices, enhancing interpretation of electronic structures and ARPES data in complex materials.

Contribution

It develops a generalized fold2Bloch package supporting arbitrary transformations, rotations, and various cell types, improving band unfolding capabilities beyond previous limitations.

Findings

Successfully unfolded Sr2IrO4 band structure and compared with ARPES data.

Highlighted importance of unfolding for interpreting SrIrO3 ARPES measurements.

Provided publicly available code and utilities for broader use.

Abstract

Unfolding of a supercell band structure into a primitive Brillouin zone is important for understanding implications of structural distortions, disorder, defects, solid solutions on materials electronic structure. Necessity of the band unfolding is also recognised in interpretation of angle-resolved photoemission spectroscopy (ARPES) measurements. We describe an extension of the fold2Bloch package by implementing an arbitrary transformation matrix used to establish a relation between primitive cell and supercell. This development allows us to overcome limitations of supercells constructed exclusively by scaling of primitive cell lattice vectors. It becomes possible to transform between primitive and conventional cells as well as include rotations. The fold2Bloch is publicaly available from a GitHub repository as a FORTRAN code. It interfaces with the all-electron full-potential WIEN2k and the pseudopotential VASP density functional theory packages. The fold2Bloch is supplemented by additional pre- and post-processing utilities that aid in generating k points in the supercell (such that they later fall onto a desired path in the primitive Brillouin zone after unfolding) and plotting the unfolded band structure. We selected Sr$_2$IrO$_4$ as an illustrative example and, for the first time, present its properly unfolded band structure in direct comparison with ARPES measurements. In addition, critical importance of the band unfolding for interpretation of SrIrO$_3$ ARPES data is illustrated and discussed as a perspective.