subroutine allocate_sites(this, n_sites)
! do we want to
class(lattice) :: this
integer, intent(in) :: n_sites
character(*), parameter :: this_routine = "allocate_sites"
if (allocated(this%sites)) then
call stop_all(this_routine, "sites are already allocated!")
end if
if (n_sites < 1) then
call stop_all(this_routine, "0 or negative number of sites!")
else
! for now it is fine to allocate the sites just as "normal"
! sites and not as bath/impurity sites..
! BUT: keep this in mind!
allocate(this%sites(n_sites))
end if
end subroutine allocate_sites