c	note that in fort.24_nc, the zero count 
c	energy is set to 4. other than 10 in our paper.

       open(unit=20,file=fpath(1:ifpath)//'/sparks_contact',
     &               status='old')
        read(20,*) rcut,i1,ncbin
           do i=1,20
              do j=1,ncbin
              read(20,*) potnc(i,j)
              enddo
           enddo
        close(20)