def _mop_line(settings):
    """
    Formats `settings` into a MOPAC input string.

    Parameters
    ----------
    settings : :class:`dict`
        Dictionary defined in :func:`mopac_opt`, where all the run
        details are defined.

    Returns
    -------
    :class:`str`
        String containing all the MOPAC keywords correctly formatted
        for the input file.

    """

    # Generate an empty string
    mopac_run_str = ""

    # Add Hamiltonian info
    mopac_run_str = mopac_run_str + settings['hamiltonian']
    # Forcing a single point calculation
    mopac_run_str = mopac_run_str + ' NOOPT '
    # Add EPS info
    eps_info = ' EPS={} '.format(settings['eps'])
    mopac_run_str = mopac_run_str + eps_info
    # Add Charge info
    charge_info = ' CHARGE={} '.format(settings['charge'])
    mopac_run_str = mopac_run_str + charge_info

    return mopac_run_str