!-------------------------------------------------------------------
    ! function  : pfunc
    !
    ! package   : Li3 Potential
    !
    ! Language  : Fortran 77 - freeform
    !
    ! author    : F. Colavecchia (flavioc@lanl.gov)
    !
    ! date      : 03/10/03       version:
    ! revision  :                version:
    !
    ! purpose   :  Compute the P function eq. (18) of the paper JCP 118 5484 (2003).
    !
    ! input     :  t  -> (dim=3) integrity basis eq. (16)
    !              x  -> (dim=n) vector of coefficients of the expansion (20).
    !              n  -> number of coefficients 
    !
    ! output    :  pfunc -> P function eq. (18)
    !
    !-------------------------------------------------------------------

      real*8 function Pfunc(t,x,n)
      implicit none
      integer n
      real*8 t(3),x(n)


      real*8 tmp1
      integer i
      
      tmp1 = 1d0-tanh(t(1)*x(2)/2d0)
      Pfunc = tmp1
      
      return
      end

    !-------------------------------------------------------------------
    ! subroutine: dPfunc
    !
    ! package   : Li3 Potential
    !
    ! Language  : Fortran 77 - freeform
    !
    ! author    : F. Colavecchia (flavioc@lanl.gov)
    !
    ! date      : 03/10/03       version:
    ! revision  :                version:
    !
    ! purpose   :  Compute the gradient respect to
    !              the parameters of P function eq. (18) of the paper JCP 118 5484 (2003)
    !
    ! input     :  t  -> (dim=3) integrity basis eq. (16)
    !              x  -> (dim=n) vector of coefficients of the expansion (20).
    !              n  -> number of coefficients 
    !
    ! output    :  grad -> gradient of P function eq. (18)
    !
    !-------------------------------------------------------------------
      subroutine dPfunc(t,x,grad,n)
      implicit none
      integer n
      real*8 t(3),x(n),grad(n)
      
      
      real*8 dtmp
      integer i
      
      dtmp = -t(1)/2d0*(1d0/cosh(t(1)*x(2)/2d0))**2d0
      grad(2) = dtmp    
      
      return
      end