Solving the DHF equations

[lelemmen]

We would like to implement and extend our current RHF routines in order to support Dirac- HF calculations.

Which basissets are used in these calculations? Or do we 'incorporate physics' (i.e. the magnetic/kinetic balance condition) in the basis functions through the one- and two-electron integrals immediately?

[lelemmen]

Since we've invested so much on compile-time correctness, we should make sure that the foundational relativistic objects are implemented first!