Unfolding method for the first-principles LCAO electronic structure calculations

TL;DR

This paper extends the unfolding method for electronic band structure analysis from Wannier functions to the LCAO basis, enabling detailed investigation of symmetry-breaking effects such as surfaces and impurities.

Contribution

The authors generalize the unfolding method to the LCAO basis, accounting for non-orthogonality, and demonstrate its effectiveness with calculations on ZrB2 slabs.

Findings

Unfolded spectral weight can be accurately calculated using the generalized formula.

The method reveals strong spectral broadening in the out-of-plane direction of ZrB2.

LCAO basis invariance simplifies the unfolding process for systems with symmetry breakers.

Abstract

Unfolding the band structure of a supercell to a normal cell enables us to investigate how symmetry breakers such as surfaces and impurities perturb the band structure of the normal cell. We generalize the unfolding method, originally developed based on Wannier functions, to the linear combination of atomic orbitals (LCAO) method, and present a general formula to calculate the unfolded spectral weight. The LCAO basis set is ideal for the unfolding method because of the invariance that basis functions allocated to each atomic species are invariant regardless of existence of surface and impurity. The unfolded spectral weight is well defined by the property of the LCAO basis functions. In exchange for the property, the non-orthogonality of the LCAO basis functions has to be taken into account. We show how the non-orthogonality can be properly incorporated in the general formula. As an illustration of the method, we calculate the dispersive quantized spectral weight of ZrB2 slab and show strong spectral broadening in the out-of-plane direction, demonstrating the usefulness of the unfolding method.