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[Bug Fix] input parameter exx_fraction ineffective when using CP

Hsin-Yu Ko requested to merge hsin-yu_ko_public/q-e:hyk.fix_exx_fraction_init into develop

Dear All,

I came across an issue with the exx_fraction parameter in the CP program. The issue is that when this parameter is set, CP does not change the internal mixing fraction used in the hybrid DFT calculation. As simple reproducer can be found here: reproducer.tar.

This issue originates from missing the initialization call "xclib_set_exx_fraction" in CPV/src/input.f90 (when compared against PWSCF). To fix this issue, please find in this MR a few changes in CPV/src/input.f90 for your consideration:

  • inclusion of the missing xclib_set_exx_fraction call
  • a test suite instance based on the reproducer (modified from the existing cp_h2o_exx instance)

In addition, I also added the screening_parameter initialization which seems to be also absent in CPV/src/input.f90. This additional patch is for future support of range-separated hybrid functionals in CP (which Robert DiStasio, Ju-an Zhang, and I hope to check-in in the near future).

Please let me know if you have questions or suggestion. Thank you very much!

Best, Hsin-Yu

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