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Crystal symmetry; Density functional theory; Group theory; Density-functional-theory; Full potential local orbitals; Function approaches; Local description; Localised; Orthonormal; Space-group symmetry; Symmetry properties; Trial functions; Wannier functions; Wave functions
Abstract:
To obtain a local description with a small basis size from density functional theory codes often a transformation to a local orthonormal Wannier function basis is desirable. In order to do so while enforcing the constraints of the space group symmetry the symmetry conserving maximally projected Wannier functions (SCMPWF) approach has been implemented in the full potential-local orbital code, FPLO. SCMPWFs are obtained from the initial step of the maximally localized Wannier function algorithm, projecting a subset of wave functions onto a set of suitably chosen local trial functions with prescribed symmetry properties with subsequent orthonormalization. The particular nature of the local orbitals in FPLO makes them an ideal set of projectors since they are constructed to be a small basis adapted to the occupied sector and the lowest-lying unoccupied states. While in many cases projection onto the FPLO basis orbitals is sufficient, the option is there to choose particular local linear combinations as projectors, in order to treat cases of bond centered Wannier functions. This choice turns out to lead to very localized Wannier functions, which obey the space group symmetry of the crystal by construction. Furthermore we discuss the interplay of the Berry connection and position operator and especially its possible approximation, symmetries, and the optimal choice of Bloch sum phase gauge in cases where the basis is not explicitly known. We also introduce various features, which are accessible via the FPLO implementation of SCMPWFs, discuss and compare performance and provide example applications. © 2023 American Physical Society.
