quantum-espresso/PP/examples/example07

This example shows how to use DFT+U with Hubbard projectors built
using (maximally localized) Wannier functions (WFs) from Wannier90.

To do this, we use the interface between Wannier90 and PW, which is 
implemented in wannier2pw.x.
This interface writes the selected WFs in files *.hub in the temporary directory.
The PW code then reads these *.hub files to perform DFT+U(WFs) calculations.
In order to activate this interface, the user must specify hubbard = .true. in the input file
of the wannier2pw.x program. 
For more details about the interface, please see the Appendix C in this paper:
A. Carta, I. Timrov, P. Mlkvik, A. Hampel, C. Ederer, arXiv:2411.03937.
Please cite this paper in publications and presentations arising from 
the use of this interface.

IMPORTANT NOTES:

- The interface supports k-points pools parallelization. This is to be consistent    
  with the other steps above if they use k-points pools parallelization. 
  Importantly, for ALL steps below (except steps 3 and 5 below), use CONSISTENTLY EXACTLY 
  THE SAME number of cores and k-points pools. If you do not do that, the results will be wrong.
- In order to run these examples, please compile the Wannier90 code and copy the
  wannier90.x executable to QE/bin

********************************************************************

TiO2 (spin-unpolarized insulator): run_example1 and reference1/

Steps:
1. Run the SCF ground-state calculation:
   pw.x < TiO2.scf.in > TiO2.scf.out

2. Run the NSCF ground-state calculation (disable symmetry!):
   pw.x < TiO2.nscf.in > TiO2.nscf.out

3. Run the pre-processing calculation using Wannier90:
   wannier90.x -pp TiO2

4. Run PW2WANNIER90 to generate the matrices Mmn and Amn which
   are needed in the next step for Wannier90:
   pw2wannier90.x < TiO2.pw2wan.in > TiO2.pw2wan.out

5. Run Wannier90 to generate the WFs:
   wannier90.x TiO2

6. Use the interface implemented in WANNIER2PW to use selected WFs 
   as Hubbard projectors and write them to files *.hub:
   wannier2pw.x < TiO2.wan2pw.in > TiO2.wan2pw.out

7. Run the SCF ground-state calculation using DFT+U(WFs):
   pw.x < TiO2.scf-wan.in > TiO2.scf-wan.out

**********************************************************************

MnO (spin-polarized insulator): run_example2 and reference2/

Steps:
1. Run the SCF ground-state calculation:
   pw.x < MnO.scf.in > MnO.scf.out

2. Run the NSCF ground-state calculation (disable symmetry!):
   pw.x < MnO.nscf.in > MnO.nscf.out

3. Run the pre-processing calculation using Wannier90 
   separately for the spin up and spin down components:
   wannier90.x -pp MnO_up
   wannier90.x -pp MnO_down

4. Run PW2WANNIER90 to generate the matrices Mmn and Amn which
   are needed in the next step for Wannier90 (separately for 
   the spin up and spin down components):
   pw2wannier90.x < MnO_up.pw2wan.in > MnO_up.pw2wan.out
   pw2wannier90.x < MnO_down.pw2wan.in > MnO_down.pw2wan.out

5. Run Wannier90 to generate the WFs separately for the spin up 
   and spin down components:
   wannier90.x MnO_up
   wannier90.x MnO_down

6. Use the interface implemented in WANNIER2PW to use selected WFs 
   as Hubbard projectors and write them to files *.hub (separately 
   for the spin up and spin down components):
   wannier2pw.x < MnO_up.wan2pw.in > MnO_up.wan2pw.out
   wannier2pw.x < MnO_down.wan2pw.in > MnO_down.wan2pw.out

7. Run the SCF ground-state calculation using DFT+U(WFs):
   pw.x < MnO.scf-wan.in > MnO.scf-wan.out

**********************************************************************