HOW TO USE GAU-PBE HYBRID FUNCTIONAL?
 keyword is input_dft='gaupbe' and it should be used simultaneouly with 
 keyword exxdiv_treatment='none' and x_gamma_extrapolation = .false.
 for example,

    input_dft='gaupbe', 
    exxdiv_treatment='none'
    x_gamma_extrapolation = .false.

gau-pbe hybrid functional is free from integrable singularity problem, which
enables to decrease k and q grids compared with other hybrid functionals.

  Please report problems and suggestions to QE developers (in particolar:
  Jong-Won Song <joshua.sjw@gmail.com>
  Stefano de Gironcoli <degironc@sissa.it>,
  and keep in mind that this feature is still experimental.