Brillouin-zone sampling

TODO: describe why we need to do \(\int_{BZ}d\vec{k} \ldots\)

Here’s an example input file for silicon

# Diamond-cubic silicon
lattice:
  system: cubic
  modification: face-centered
  a: 10.26  # bohrs

ions:
  pseudopotentials:
    - ../../../JDFTx/build_testing/pseudopotentials/SG15/$ID_ONCV_PBE.upf
  coordinates:
    - [Si, 0.125, 0.07, 0.01]
    - [Si, 0.375, 0.32, 0.26]

electrons:
  k-mesh:
    offset: [0.5, 0.5, 0.5] #Monkhorst-Pack
    size: [8, 8, 8]

grid:
  ke-cutoff: 100

checkpoint: null  # disable reading checkpoint
checkpoint-out: Si.h5  # but still create it