libxc version 7.1.2
S. Lehtola, C. Steigemann, M. J. T. Oliveira, and M. A. L. Marques,  SoftwareX 7, 1–5 (2018)
doi: 10.1016/j.softx.2017.11.002

   func_id: 130                 
      name: gga_c_pbe                
    family: XC_FAMILY_GGA       
      kind: XC_CORRELATION           
   comment: Perdew, Burke & Ernzerhof

Reference(s):
  *) J. P. Perdew, K. Burke, and M. Ernzerhof,  Phys. Rev. Lett. 77, 3865 (1996)
     doi: 10.1103/PhysRevLett.77.3865
     bibtex key: Perdew1996_3865
  *) J. P. Perdew, K. Burke, and M. Ernzerhof,  Phys. Rev. Lett. 78, 1396 (1997)
     doi: 10.1103/PhysRevLett.78.1396
     bibtex key: Perdew1997_1396

Implementation has support for:
  *) energy
  *) first derivative
  *) second derivative

Default thresholds:
density: 1.000000e-12
   zeta: 2.220446e-16
  sigma: 1.000000e-16

Functional has 4 external parameters:
idx         value     name description
  0  6.672455e-02    _beta beta constant
  1  3.109069e-02   _gamma (1 - ln(2))/Pi^2 in the PBE
  2  1.000000e+00       _B Multiplies the A t^2 term. Used in the SPBE functional
  3  1.000000e+00  _tscale Scaling for t, used in the BKL functionals
