Quantum Unfolding: A program for unfolding electronic energy bands of materials

Abstract

We present Quantum Unfolding, a Fortran90 program for unfolding first-principles electronic energy bands. It unfolds energy bands accurately by handling the Fourier components of Bloch wavefunctions, which are reconstructed from Wannier functions from Wannier90. Due to the wide application of Wannier90 package and the possibility of focusing only on the most important energy bands, the present code works very conveniently. Program summaryProgram title: Quantum UnfoldingCatalogue identifier: AEVF_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEVF_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 38350No. of bytes in distributed program, including test data, etc.: 1374243Distribution format: tar.gzProgramming language: Fortran 90.Computer: Any computer architecture.Operating system: Linux, Windows.RAM: System dependent, from several MB to several GBClassification: 7.3.External routines: Lapack ffyw3, QuantumEspresso.Subprograms used:Cat IdTitleReferenceAEAK_v2_0wannier90CPC 185(2014)2309Nature of problem:The Brillouin zone of a supercell is smaller than that of a primary cell. It makes the supercell energy bands more crowded. The crowded energy bands are outright difficult, if not impossible, to be compared with experimental results directly. Besides, the intra-supercell translation symmetries are hidden in the supercell band structure calculations. In order to compare with experiments and catch the hidden symmetries, we have to unfold the supercell energy bands into the corresponding primary-cell Brillouin zone.Solution method:The electron wavefunction is reconstructed from Wannier functions and Hamiltonian parameters, which are produced by Wannier90 package. Then by using fast Fourier transformation (FFT), we get the Fourier components of the reconstructed wavefunction. The unfolding weight is calculated from the Fourier components, based on group theory and its special form for plane-wave basis.Unusual features:Simple and user-friendly input system. Great efficiency and high unfolding speed.Running time:System dependent, from a few minutes to several hours.