function userfunc(x)
      real*8 userfunc,x
      userfunc=0.0
      end
c
c
c     coulomb force 
      function userfunc1(x)
      real*8 userfunc1,x
      userfunc1=x**-1.5
      end
c
c
c     coulomb potentail
      function userfunc2(x)
      real*8 userfunc2,x
      userfunc2=x**-0.5
      end
c
c
c     LJ force 
      function userfunc3(x)
      real*8 userfunc3,x
      userfunc3=2.0 * x**-7.0 - x**-4.0
      end
c
c
c     LJ potential
      function userfunc4(x)
      real*8 userfunc4,x
      userfunc4=x**-6.0 - x**-3.0
      end
c
c
      function userfunc5(x)
      real*8 userfunc5,x
      userfunc5=0.0
      end
c
c
      function userfunc6(x)
      real*8 userfunc6,x
      userfunc6=0.0
      end
c
c
c     Ewald real space force
      function userfunc7(x)
      real*8 userfunc7,x
      userfunc7=1.12837916709551257390 * exp(-x) * x**-1.0 
     -          + erfc(sqrt(x)) * x**-1.5
      end
c
c
c     Ewald real space potential
      function userfunc8(x)
      real*8 userfunc8,x
      userfunc8=erfc(sqrt(x)) * x**-0.5
      end
c
c
      function userfunc9(x)
      real*8 userfunc9,x
      userfunc9=0.0
      end
c
c
      function userfunc10(x)
      real*8 userfunc10,x
      userfunc10=0.0
      end
c
c
      function userfunc11(x)
      real*8 userfunc11,x
      userfunc11=0.0
      end
c
c
      function userfunc12(x)
      real*8 userfunc12,x
      userfunc12=0.0
      end