Overlap integrals for a pair of basis sets

[tovrstra]

@BradenDKelly It's becoming a daily routine. :) I did already try some other performance improvements, but further (significant) speedups without drastic code changes seem difficult to accomplish. For example, just vectorizing code inside the current bottleneck (compute_overlap_gaussian_1d) is not helpful because the arrays already too small at that level. Anyway, before doing anything more substantial, I'd figured it would be useful to add a feature to the overlap code, i.e. to compute overlaps between two basis sets, which are needed in #146 and #175. When trying to make things more efficient, we should not make it impossible to support this feature.

[codecov]

Codecov Report

Merging #238 (536ee5c) into master (aaa6118) will increase coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #238      +/-   ##
==========================================
+ Coverage   95.07%   95.15%   +0.08%     
==========================================
  Files          72       72              
  Lines        7371     7496     +125     
  Branches      985      999      +14     
==========================================
+ Hits         7008     7133     +125     
  Misses        175      175              
  Partials      188      188              

Impacted Files	Coverage Δ
iodata/overlap.py	100.00% <100.00%> (ø)
iodata/test/test_overlap.py	100.00% <100.00%> (ø)
iodata/api.py	85.91% <0.00%> (-0.58%)	⬇️
iodata/formats/mol2.py	89.71% <0.00%> (-0.19%)	⬇️
iodata/formats/fchk.py	90.17% <0.00%> (-0.06%)	⬇️
iodata/periodic.py	100.00% <0.00%> (ø)
iodata/formats/pdb.py	100.00% <0.00%> (ø)
iodata/inputs/orca.py	100.00% <0.00%> (ø)
iodata/test/test_fchk.py	100.00% <0.00%> (ø)
iodata/test/test_mol2.py	100.00% <0.00%> (ø)
... and 4 more

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[BradenDKelly]

There does seem to be quite abit of overlap between additions... dun dun dun :)

Will look this over, unfortunately, probably on the weekend. Want to look it over carefully. Need to create and run some workflows involving the latest additions to iodata first though.

[tovrstra]

No problem. Take your time.

[BradenDKelly]

I think this is good to go. Should not have said take my time, I totally lost track :S

[tovrstra]

No problem. Thanks for reviewing!