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+c*****************************************************************
+c*****************************************************************
+c*****************************************************************
+c                             GGA 
+c        The Generalized Gradient Approximation
+
+c  GGA is a way to improve the local spin density approximation
+c  by adding nonlocal gradients in the evaluation of the exchange-
+c  correlation energy and potential. These functions and subroutines 
+c  are based on programs made by John Perdew, Tulane University,
+c  New Orleans, Louisiana, USA. Email: PY03APF%music.tcs.tulane.edu
+c  The modifications necessary to fit them to the atom program was
+c  made by Tomas Holmquist 1993 (so now you know who to blame). 
+c  Email: tomash@fy.chalmers.se
+c  A more thorough description of the GGA used may be found in 
+c  J.P. Perdew et al, Phys. Rev. B  (46) 1992 pp. 6671-6687.
+
+c  The GGA package is:
+
+c         function deriv
+c         subroutine grad
+c         subroutine grabgr
+c         subroutine laplac
+c         subroutine spline
+c         subroutine splint
+c     subroutine ggaexc
+c         subroutine exchen
+c         subroutine ldaec
+c         subroutine gcor
+c         subroutine ggaec
+c     subroutine ggauxc
+c         subroutine exchpt
+c         subroutine ldauc
+c         subroutine ggauc
+
+c  The grad, grabgr, and laplace subroutines uses the function deriv
+c  to calculate different derivatives with respect to the radial 
+c  coordinate r. Spline and splint calculates the cubic spline 
+c  interpolation which is used in function deriv.
+c  The two main subprograms, ggaexc and ggauxc, calculates
+c  the exchange-correlation energy and potential respectively.
+c  The other subroutines are modified versions of Perdew's program.
+
+c*****************************************************************
+c*****************************************************************