Abstract
Present day computing facilities allow for first-principles density functional theory studies of complex physical and chemical phenomena. Often such calculations are linked to large supercells to adequately model the desired property. However, supercells are associated with small Brillouin zones in the reciprocal space, leading to folded electronic eigenstates that make the analysis and interpretation extremely challenging. Various techniques have been proposed and developed to reconstruct the electronic band structures of super cells unfolded into the reciprocal space of an ideal primitive cell. Here we propose an unfolding scheme embedded directly in the Vienna Ab initio Simulation Package (VASP) that requires modest computational resources and allows for an automatized mapping from the reciprocal space of the supercell to the primitive cell Brillouin zone. This algorithm can compute band structures, Fermi surfaces, and spectral functions by using an integrated postprocessing tool (bands4vasp). Here the method is applied to a selected variety of complex physical situations: the effect of doping on the band dispersion in the BaFe2(1–x)Ru2xAs2 superconductor, the interaction between adsorbates and polaronic states on the TiO2(110) surface, and the band splitting induced by noncollinear spin fluctuations in EuCd2As2.
Highlights
Material science simulations adopting periodic boundary conditions in the framework of the density functional theory (DFT) may require large unit cells to model long or broken periodicity in crystals
Whereas well-developed facilities and efficient DFT packages are capable of dealing with hundreds and even thousands of atoms in large cells, the analysis of the electronic properties gets complicated by the shrinking of the Brillouin zone (BZ) and the consequent folding of the eigenstates in the reciprocal space.[3]
This material is a good testbed because much reference data are available in literature.[19−21] We take this opportunity to describe features included in the postprocessing bands4vasp package, such as the visualization of band structures, the Fermi surfaces and spectral function, and the calculation of Fermi wave vectors (Section 3.1)
Summary
Material science simulations adopting periodic boundary conditions in the framework of the density functional theory (DFT) may require large unit cells to model long or broken periodicity in crystals. The intricate supercell states can be unfolded back into the larger BZ of the primitive cell by applying the unfolding technique.[3,6−10] This technique is based on the projection PKm of the supercell eigenstates |Km⟩ on the primitive cell eigenstates |kn⟩
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