Abstract
In plane-wave density functional theory codes, defects and incommensurate structures are usually represented in supercells. However, interpretation of E versus band structures is most effective within the primitive cell, where comparison to ideal structures and spectroscopy experiments are most natural. Popescu and Zunger recently described a method to derive effective band structures (EBS) from supercell calculations in the context of random alloys. In this paper, we present bs_sc2pc, an implementation of this method in the CASTEP code, which generates an EBS using the structural data of the supercell and the underlying primitive cell with symmetry considerations handled automatically. We demonstrate the functionality of our implementation in three test cases illustrating the efficacy of this scheme for capturing the effect of vacancies, substitutions and lattice mismatch on effective primitive cell band structures.
Highlights
E versus k band structures and derived quantities such as effective mass or group velocity are valuable concepts to describe the electronic properties of crystalline materials
The E(k) dispersion is usually evaluated along certain high-symmetry paths in the Brillouin zone (BZ) of a few-atom primitive cell
We demonstrated the bs sc2pc program to determine effective band structures for supercells, based on the band structure unfolding method described by Popescu [8]
Summary
E versus k band structures and derived quantities such as effective mass or group velocity are valuable concepts to describe the electronic properties of crystalline materials. The E(k) dispersion is usually evaluated along certain high-symmetry paths in the Brillouin zone (BZ) of a few-atom primitive cell (pc) These small cells cannot usually accommodate defects at experimentally relevant concentrations, or represent composite structures with significant lattice mismatch. In plane wave DFT [1, 2], which requires periodicity, such structures are usually represented in supercells (SC). This corresponds to a BZ with a fraction of the size of that of the primitive cell and a multiple of the number of bands. The scheme of Popescu and Zunger [6, 8] is attractive in the context of plane-wave pseudopotential calculations They described their method primarily in the context of random alloys.
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