In case of exchange-only Kohn-Sham DFT calcuations, the code is now printing...

Description

In case of exchange-only Kohn-Sham DFT calculations, the code is now printing the exchange energy computed from the orbitals (or density) and from the potential, using the virial relation.

The exchange energy for the FBE exchange potential is now computed from the orbitals, such that it can be compared to the one of coming from the virial relation.

News snippet

Computing the exchange-virial expression for exchange-only DFT calculations.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.