=====================================================================
revPBE
=====================================================================
To construct the revPBE functional you exchange the parameter
declation in subroutine EXCHPBE:

parameter(um=0.2195149727645171d0,uk=0.8040d0,ul=um/uk)

with

parameter(um=0.2195149727645171d0,uk=1.2450d0,ul=um/uk)



=====================================================================
RPBE
=====================================================================
To construct the RPBE functional you keep the parameter declaration
of uk=0.8040d0 and substitute the lines in subroutine EXCHPBE:

      P0=1.d0+ul*S2
      FxPBE = 1d0+uk-uk/P0
      EX = exunif*FxPBE
c----------------------------------------------------------------------
c----------------------------------------------------------------------
C  ENERGY DONE. NOW THE POTENTIAL:
c  find first derivatives of Fx w.r.t s.
c  Fs=(1/s)*d FxPBE/ ds
c  Fss=d Fs/ds
      Fs=2.d0*um/(P0*P0)
      Fss=-4.d0*ul*S*Fs/P0


with

c This is the RPBE functional
      P0=exp(-ul*S2)
      FxPBE = 1d0+uk*(1.0d0-P0)
      EX = exunif*FxPBE
c----------------------------------------------------------------------
c----------------------------------------------------------------------
C  ENERGY DONE. NOW THE POTENTIAL:
c  find first derivatives of Fx w.r.t s.
c  Fs=(1/s)*d FxPBE/ ds
c  Fss=d Fs/ds
      Fs=2.d0*um*P0
      Fss=-2.d0*ul*S*Fs