The below is the non-relativistic solution (DOI: 10.14469/hpc/2161), derived from a full-electron basis set for I (6-311G(d,p) as obtained from https://bse.pnl.gov/bse/portal).

Basins 8 and 9 have 2.21e each and subtend an angle of 168° at the central iodine. The other difference is that basins 10 and 15 for BrF_{3} (the anomeric anti-periplanar effect to one Br-F bond) are not apparent for IF_{3}.

A wavefunction where the all-electron basis set is replaced by one with a effective-core for the relativistic component (thus the relativistic contraction is absorbed into this calculation, Def2-TZVPP, DOI: 10.14469/hpc/2162) gives the 8/9 basin populations as 2.36e, which is more consistent with the trend Cl => Br => I and an angle subtended at I of 153°.

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