anchor.diff:  integer, allocatable :: connected_sites(:,:) ! (2ndim, nbasis)
   
   ! True if any site is its own periodic image.
  -! This is the case if one dimension (or more) has only one site per crystal
  +! This is the case if one dimension (or more) has only one site per crystalisystem
   ! cell.  If so then the an orbital can incur a kinetic interaction with itself.
   ! This is the only way that the integral < i | T | i >, where i is a basis
   ! function centred on a lattice site, can be non-zero.
  
positive.code: 
          tmat = 0
          connected_orbs = 0
  
          ! Form all lattice vectors
          select case(ndim)
  
negative.code:                                 ! connected_orbs does not contain self-connections 
                                  ! due to the periodic boundary conditions.
                                  call set_orb(connected_orbs(:,i),j)
                                  if (isystem == 2) call set_orb(connected_orbs(:,i+1),j+1)                      
                                  call set_orb(connected_orbs(:,j),i)
                                  if (isystem == 2) call set_orb(connected_orbs(:,j+1),i+1)
                              end if
                          end if
                      end if
  