anchor.diff:          use utils, only: get_free_unit
           use checking, only: check_allocate
           use errors, only: stop_all
  +
  +        use, intrinsic :: iso_fortran_env
   
           ! System data
           ! We don't know how many orbitals we have until we read in the FCI
  
positive.code:         call init_molecular_integrals()
  
          ! read integrals and eigenvalues
          do
              ! loop over lines.
              read (ir,*, iostat=ios) x, i, a, j, b
              if (ios < 0) exit ! reached end of file
              if (ios > 0) call stop_all('read_input','Problem reading input.')
              if (.not.uhf) then
                  ! Working in spin-orbitals but FCIDUMP is in spatial orbitals.
                  i = i*2
                  j = j*2
                  a = a*2
  
negative.code: module read_in_system
  
  ! Module for reading in and manipulating integral files which entirely define
  ! the Hamiltonian corresponding to a 'real' system.
  
  use const
  
  