REAL*8 FUNCTION D2VNENE(rnene)
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c	This subroutine computes the second derivitive of the ne-ne 
c	potentail. 
c	
c	Date. 8/1/20001		by. Keming Zhang
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c  original Aziz-Slaman routine used reduced units.  This version has
c  r and v in atomic units.  Russ Pack 98/5/5
      IMPLICIT None
	REAL*8 epsnene, rmnene, rnene, UA, A, UB, Alpha, beta
      REAL*8 DUB, DDUB, UC, DUC, DDUC, C6, C8, C10, D, D1x, DD1X, DDD1X
      REAL*8 C, UD, DUD, DDUD, CHNGE, B, EN, EM 
      REAL*8 x, x2, x3, x6, x7, x8, x9, x10, x11, x12     
      integer icall
      character*8 procname
      parameter (procname='vnene   ')
c  ------1---------2---------3---------4---------5---------6---------7--
      COMMON/POTNENE/A,ALPHA,C6,C8,C10,C,D,CHNGE,B,BETA,EN,EM
      data icall /0/
      save
c  determine parameters on first call.
      if (icall.eq.0) then
         call nenedat
c  well depth and rm, both in au.
         epsnene = 1.337985194d-04
         rmnene = 5.841143031d0
         icall=1
      end if
c  start here on further calls

      x = rnene/rmnene
      if(x.gt.1.d04) return
      X2=X*X
	X3=X2*X
      X6=X3*X3
	X7=X6*X
      X8=X7*X
	X9=X8*X
      X10=X9*X
	X11=X10*X
	X12=X11*X
      UA=A
      UB=ALPHA*X-BETA*X*X
	IF(174.D0<UB) THEN 
		UB=174.D0
		DUB=0
		DDUB=0	
	ELSE
		DUB=ALPHA-2*BETA*X
		DDUB=-2*BETA	
	END IF

      UC=C6/X6+C8/X8+C10/X10
	DUC=-6*C6/X7-8*C8/X9-10*C10/X11
	DDUC=42*C6/X8+72*C8/X10+110*C10/X12

      D1X=D/X-1.D0
	DD1X=-D/X2
	DDD1X=2*D/X3

	IF(174.D0.LT.C*D1X*D1X)THEN
		UD=DEXP(-174.D0)
		DUD=0d0
		DDUD=0d0
	Else
		UD=DEXP(-C*D1X*D1X)
		DUD=-2*C*D1X*DD1X*UD
		DDUD=-2*C*(DD1X*DD1X*UD+D1X*DDD1X*UD+D1X*DD1X*DUD)
	End if
	
	If(X.GE.CHNGE) then
		D2VNENE=UA* DEXP(-UB)*(DUB*DUB-DDUB) - DDUC
	Else
		D2VNENE=UA* DEXP(-UB)*(DUB*DUB-DDUB) - 
     >					(DDUC*UD+2*DUC*DUD+UC*DDUD) 
	End if
	
      D2VNENE = epsnene*D2VNENE/rmnene/rmnene
	
      RETURN
      END