Keywords: user_guide

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## 4.2 Band structure, Fermi surface

The code `bands.x` reads data file(s), extracts eigenvalues, regroups them into bands (the algorithm used to order bands and to resolve crossings may not work in all circumstances, though). The output is written to a file in a simple format that can be directly read and converted to plottable format by auxiliary code `plotband.x`. Unpredictable plots may results if k-points are not in sequence along lines, or if two consecutive points are the same. The code `bands.x` performs as well a symmetry analysis of the band structure. For a complete input description, see `Doc/INPUT_bands.*`. See Example 01, Example 04 and Example 06 for simple band plots.

The calculation of Fermi surface can be performed using code `fs.x`. The resulting file in .bxsf format can be read and plotted using XCrySDen. See Example 02 for an example of Fermi surface visualization (Ni, including the spin-polarized case).