quantum-espresso/PW/examples/gammaDFT_example

These examples show how to perform gammaDFT calculations to stabilize
the hole polaron in MgO according to

S. Falletta and A. Pasquarello, Phys. Rev. Lett. 129, 126401 (2022)
S. Falletta and A. Pasquarello, Phys. Rev. B 106, 125119, (2022)

The examples show three different practical cases:

- example1: gammaDFT calculation with energy evaluation 
- example2: gammaDFT atomic relaxation without energy evaluation
- example3: gammaDFT calculation + scissor operator for bands

For MgO, we use gamma=1.96, which enforces the piece-wise linearity 
condition and thus suppresses the many-body self-interaction of the 
polaron state.

The use of the scissor operator is recommended to avoid resonances
of the polaron level with the bands. For electron polarons, one might
shift down in energy the valence band. For hole polarons, one might
shift up in energy the conduction band.