# FPLO

The FPLO^{®} package is a full-potential local-orbital code [1] [2] to solve the Kohn-Sham equations [5] on a regular lattice or with free boundary conditions (finite systems). Relativistic effects are treated either in a scalar-relativistic or a full 4-component formalism [3]. Available functionals are LSDA, GGA (PBE 96) and LSDA/GGA+U. [4]. Orbital polarization correction can be applied.

Much effort has been spent to achieve a level of numerical accuracy which is comparable to advanced full-potential LAPW implementations, though the basis set is considerably smaller [6]. This makes highly accurate full-potential calculations for elementary cells of up to 300 atoms feasible on single-CPU machines and is a good starting point for approaches beyond standard DFT.

The FPLO band structure can be wannierized [7], which allows model extraction and post processing, in particular the calculation of topological properties, topological surface states, dHvA spectra and more using the in-build PYTHON interface (pyfplo).

- References
- [1] K. Koepernik and H. Eschrig, Phys. Rev. B 59, 1743 (1999).

[2] I. Opahle, K. Koepernik, and H. Eschrig, Phys. Rev. B 60, 14035 (1999).

[3] H. Eschrig, M. Richter, I. Opahle, Relativistic Solid State Calculations, in: Relativistic Electronic Structure Theory, Part 2. Applications (P. Schwerdtfeger, ed.), Theoretical and Computational Chemistry, vol.14, Elsevier, 2004, pp.723–776.

[4] H. Eschrig, K. Koepernik, and I. Chaplygin, J. Solid State Chemistry 176, 482 (2003).

[5] Helmut. Eschrig: The Fundamentals of Density Functional Theory, 2nd Edition, Edition am Gutenbergplatz, Leipzig, 2003.

[6] K. Lejaeghere*et al.*, Science**351**, 1415-U81 (2016).

[7] K. Koepernik, O. Janson, Yan Sun, and J. van den Brink, Phys. Rev. B 107, 235135 (2023). Financial support by MPG, DFG, Humboldt-Foundation, EC and BMBF is gratefully acknowledged.