c2x and Elk

Elk is an all-electron GPLed LAPW DFT code.

From version 2.34c c2x can write a basic system description to a Elk-style .in file, and recognises the filename elk.in for invoking its Elk .in reader. It will also read Elk's GEOMETRY.OUT output, as well as its output files ending 3D.OUT.

Note that Elk's RHO3D.OUT is produced by sampling the density in a manner which is not guaranteed to preserve its integral. Unless the grid used is very fine, one is likely to lose, or gain, a substantial fraction of an electron, or even several electrons, for the density is a rapidly-varying function near the nuclei.

Elk can produce .bxsf files for Fermi surfaces directly. There is an example of obtaining a charge density isosurface from graphite.