quantum-espresso/PW/examples/example15

This example shows how to use pw.x to perform constrained DFT+U
calculations for FeO. The method is described in 
L. Ponet et al., npj Comput. Mater. 10, 151 (2024).

In order to peform this calculation, Quantum ESPRESSO must be 
configured with the -D__OSCDFT flag: please see the documentation
for more details at q-e/PW/Doc/INPUT_OSCDFT.def. Then one needs
to prepare the OSCDFT input file (please see below), and execute
the pw.x command with the flag -oscdft as follows:
pw.x -oscdft < FeO.scf.in > FeO.scf.out

This contrained approach is implemented inside the oxidation-state
constrained DFT (OSCDFT) framework, with the option oscdft_type = 2.

The contrained DFT+U calculation can be done in two ways:
1. By providing the eigenvalues of the target occupation matrix (see run1)

   The syntax for this first option is the following:
   TARGET_OCCUPATION_NUMBERS
   I s m eigenvalue

   Here, I is the atomic index (according to ATOMIC_POSITIONS),
         s is the spin index (1 for up, and 2 for down),
         m is the index of the eigenvalue 
         (e.g. from 1 to 5 for d electrons),
         'eigenvalue' is the target eignvalue of the occupation matrix.

2. By providing the full target occupation matrix (see run2)

   The syntax for this first option is the following:
   TARGET_OCCUPATION_NUMBERS
   I s m m' occupation

   Here, I is the atomic index (according to ATOMIC_POSITIONS),
         s is the spin index (1 for up, and 2 for down),
         m and m' are the indices of the magnetic quantum numbers 
         (e.g. from 1 to 5 for d electrons),
         'occupation' is the target occupation value.

Please see the documentation at q-e/PW/Doc/INPUT_OSCDFT.def for the
descritpion of all other input keywords in the OSCDFT input file.