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: 263                 
      name: mgga_x_scan              
    family: XC_FAMILY_MGGA      
      kind: XC_EXCHANGE              
   comment: SCAN exchange of Sun, Ruzsinszky, and Perdew

This is a pure functional with no exact exchange.

Reference(s):
  *) J. Sun, A. Ruzsinszky, and J. P. Perdew,  Phys. Rev. Lett. 115, 036402 (2015)
     doi: 10.1103/PhysRevLett.115.036402
     bibtex key: Sun2015_036402

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

Default thresholds:
density: 1.000000e-15
   zeta: 2.220446e-16
  sigma: 1.000000e-20
    tau: 1.000000e-20

Functional has 4 external parameters:
idx         value     name description
  0  6.670000e-01      _c1 c1 parameter
  1  8.000000e-01      _c2 c2 parameter
  2  1.240000e+00       _d d parameter
  3  6.500000e-02      _k1 k1 parameter
