!-------------------------------------------------------------------
    ! function  : curvepot
    !
    ! package   : potentials
    !
    ! Language  : Fortran 90
    !
    ! author    : F. Colavecchia (flavioc@lanl.gov)
    !
    ! date      : 01/29/03     version:
    ! revision  :              version:
    !
    ! purpose   :  Compute the pontential curve of arrangement arr
    !              for a internuclear distance r between the 
    !              atoms that compose the arrangement arr.
    !
    ! input     :   arr -> arrangement (1 2 3)
    !               r   -> internuclear distance, NOT mass scalesd
    !
    ! output    :    curvepot -> V_arr(r) in a.u. 
    !
    ! modules   :
    !
    !
    ! common    :
    !
    !
    ! notes     :
    !
    !-------------------------------------------------------------------


    real*8 function curvepot(arr,r)
    use pes_module
    !              pesname must contain a character string
    !              of length 20 that properly describes the potential.
    !
    implicit none
    integer arr
    real*8 r,vnene,vneh
    character(len=25) potname
    !
    ! Check for correct potential energy surface specification.
    !
    if(pesname.ne.potname)then
        write(*,*)'The potential energy surface name does not'
        write(*,*)' match the name in the potential energy surface routine.'
        write(*,*)'***error***: Execution stopped in routine curvepot'
        write(*,*) 'pesname=', pesname
        write(*,*) 'potname=', potname
        stop 'curvepot'
    end if
    if(arr.lt.1.or.arr.gt.3) then
        write(*,*) 'Invalid arrangement'
        write(*,*) 'arr =',arr
        stop 'curvepot'
    end if
    !
    !
    if(arr.eq.1) then
        curvepot = vnene(r)
    else if(arr.eq.2) then
        curvepot = vneh(r)
    else
        curvepot = vneh(r)
    end if
    !  the following is a special case
    !  v=0
    return
    end