from pathlib import Path


def create_data_dir(run_dir):
    """
    Create initial files for HADDOCK3 run.

    Returns
    -------
    pathlib.Path
        A path referring only to 'data'.
    """
    data_dir = Path(run_dir, 'data')
    data_dir.mkdir(parents=True, exist_ok=True)
    return data_dir