Check self correlations for non-monatomic pairs

[rmatsum836]

For non-monatomic pairs (oxygen-hydrogen), we shouldn't calculate any self-interactions even if self_correlation=True . This PR adds a check to compute_partial_van_hove which sets self_correlation to False if selection1 != selection2. User is warned if this happens.

Test case has also been added to check that warning is properly raised.

[jacoblumpkins]

It looks good to me. The only thing I can think of is: should the default behavior of compute_van_hove have detection built in such that it calls compute_partial_van_hove with self_correlation = False for polyatomic pairs and self_correlation = User_Input (default: True) for monoatomic pairs? Otherwise, every system with more than one atom type will print a warning on the call to compute_van_hove.

[rmatsum836]

Sounds good, something like?

for elem1, elem2 in it.combinations(...):
    if elem1 != elem2:
        compute_partial_van_hove(self_correlation=False)
   else:
        compute_partial_van_hove(self_correlation=True)

[jacoblumpkins]

Yep! Might be easier to have a boolean variable and just reference that in the existing code.

for elem1, elem2 in it.combinations(...):
    myBool = self_correlation          # User Input
    if elem1 != elem2: 
        myBool = False

    data.append(
                [
                    ...
                    self_correlation = myBool,
                    ...
                ]
            )

[rmatsum836]

Thanks for the suggestion, let me know what you think!

[jacoblumpkins]

Look's good!