Assuming #462 or similar functionality is merged, a single output directory, janus_results will be created, but repeated calculations may overwrite output files, which is consistent with current behaviour.

Ideally, we will have an (optional) way of specifying whether to use the existing output directory, or create new ones, e.g. janus_results_1, janus_results_2, etc. for each new calculation.

Some care will need to be taken about when the new directory name is determined and created, particularly in cases where calculations call other calculations, or where output files may be defined and written at different stages of the calculation, such as running different components of phonon calculations, which is why I think it's best to treat it separately to #462.