Needs testing:
- Shifted Gamma pt calc (e.g. at Baldereschi pt)
- pyscf.util.examples or pyscf.pbc.util.examples with a small database of
  models and properties obtained with various codes.  These may then be used in
  actual tests for comparison as well as in the examples section.
  > example calculations of realistic (but small) models (no low-level coding);
  > test free of external imports (ase);
  > performance (which may also be compared to other codes) benchmark;


Code doc and cleaning:
- Test infrastructure and examples for
  - K pt calcs
  - band structure
  - Gamma pt HFX
- Initial guess: check which ones are correct for PBC / PP / KSCF

Ease of calc:
- Better cutoff fn for lattice sums (from integral Schwartz condition)
- ASE DFT calculator interface

Other Functionality:
- q->0 term for (ia|jb) integral, by finite difference q calc
- UHF code and UHF initial guess (specify mag. moment for AFM)
- Gamma pt MP2
  - check q->0, compare against VASP / CP2K 
- IP/EA/EE-EOM-CCSD 
  - General spin-orb -> spin-orb -> restricted

- addon routines to compute finite size corrections to the energies

Efficiency:
- Time-reversal symmetry
  - K pts in Brillouin zone
  - Grid in FFT
- Abelian cell symmetry (See symmetry class in GPAW)
  - Lattice sums
  - Grids
- Profile code
  - Integral screening

