Change deletion move acceptance criteria for restricted insertions

[rsdefever]

Description

Update the deletion move acceptance criteria to use the inner_volume, aka, restricted insertion volume. Previously it used the volume of the full box. This is incorrect.

As currently implemented, restricted insertions should only be used if the inserted molecules cannot escape the restricted region during a simulation (e.g., impenetrable walls block off the restricted region from the remainder of the simulation box). A relevant warning was added to the user manual.

Caveat/possible future additions

It would be possible to use restricted insertions in a situation where molecules could escape the restricted region if the code was modified to only attempt deletion moves on molecules that were currently within the restricted region. At this time this feature has not been implemented and thus restricted insertions should be limited to the scenario where molecules cannot escape the restricted region.

How Has This Been Tested?

Results for SPC/E water inserted into a graphene pore were compared using restricted insertions and insertions anywhere in the box. In the latter case, the only viable insertions were in the pore due to the excluded volume of the graphene layers comprising the pore. The results were identical in both cases. With the previous version of the code, Cassandra over-estimated the number of waters in the pore. The results are also in agreement with results from GOMC.

Backward Compatibility

Full backwards compatibility is maintained.

Post Submission Checklist

Please check the fields below as they are completed

• Suitable new documentation files and/or updates to the existing docs are included.
• One or more example input decks are included.