SUBROUTINE LennardJones_Potential(r, v, vp, vpp)
USE Numeric_Kinds_Module
USE Numbers_Module
IMPLICIT NONE
SAVE
INTEGER IFirst
REAL(KIND=WP_Kind) :: De   = 3.880453448111275E-002
REAL(KIND=WP_Kind) :: re   = 5.05240520316459
INTEGER, PARAMETER :: LennardJones_Unit=8
REAL(KIND=WP_Kind) :: r, v, vp, vpp, x, x6, x12
DATA IFirst/-1/

IF(IFirst==-1)THEN
  WRITE( LennardJones_Unit,*)
  WRITE( LennardJones_Unit,*)"LennardJones Parameters"
  WRITE( LennardJones_Unit,*)"  De=",De
  WRITE( LennardJones_Unit,*)"  re=",re
ENDIF

x=re/r
x6=x**6
x12=x6**2
v=De*(x12-Two*x6)
vp=De*(-Twelve*x12/r+Twelve*x6/r)
vpp=De*(156.d0*x12/r**2-84.d0*x6/r**2)

RETURN
END SUBROUTINE LennardJones_Potential