## Fleur documentation

The Fleur code implements the all-electron full-potential linearized augmented-plane-wave (FLAPW) approach to density functional theory (DFT). It allows the calculation of properties obtainable by DFT for crystals and thin films composed of arbitrary chemical elements. For this it treats all electrons on the basis of DFT and does not rely on the pseudopotential approximation. There are also no shape approximations to the potential required. However, this comes at the cost of complex parametrizations of the calculations. The Fleur approach to this complex parametrization is the usage of an input generator that itself only requires basic structural input. Using this it generates a completely parametrized Fleur input file with material adapted default parameters. The advanced user should understand the Fleur input file and be able to modify it if needed. For this the first part of the documentation introduces the FLAPW method and connects it to its implementation in Fleur and the parameter names used in the input file.

The second part of the documentation focuses on specific calculations for the computation of different target quantities. This can be understood as a How-To.

In detail the documentation is organized as follows:

- The FLAPW method and its implementation in Fleur
- Theory Overview
- Partitioning of the unit cell and energy ranges
- Representation of valence electrons
- The LAPW basis for thin film systems
- Details on the Hamiltonian and Overlap matrix setup
- Treatment of core electrons
- Usage of symmetries
- Construction of the charge density
- Construction of the potential
- Treatment of collinear magnetism
- Spin-orbit coupling in 2nd variation
- Treatment of noncollinear magnetism
- Description of spin spirals

- Specific calculations
- Expert knowledge and Troubleshooting