def parse(atom_types_filename):
    """
    Parse ``atom_types`` file
    """
    d = {}
    with open(atom_types_filename) as f:
        for line in f:
            line = line.strip()
            if not line or line.startswith('#'):
                continue
            fields = line.split('#', 1)[0].split()
            d[fields[0].upper()] = fields[1]
    return d
