real U2(100), U1(100), U0(100)
      open (20,file="laine.xyz")
      alpha=0.01
      nt=100
      nat=100
      do i=1,100
      U1(i)=0.
      U0(i)=0.
      U2(i)=0.
      enddo
      
      U1(50)=0.1
      U0(50)=0.1
      
      do k=1,nt
      write(20,"(i5)") nat
      write(20,"('aaaaaaa')")

      do i=2,99
      U2(i)=alpha*(U1(i+1)-2.*U1(i)+U1(i-1))
     *          +2.*U1(i)-U0(i)
      enddo
      
      
      U2(1)=0.
      U2(100)=0.
      
      do i=1,100
      U0(i)=U1(i)
      U1(i)=U2(i)
      enddo
      
      do kk=1,nat
      write(20,"('H',2f15.5,'  0.')") kk*0.1,U2(kk)*100.
      enddo
      
      enddo
      
 
      stop
      end