The Ar Isoelectronic Series

As we go further down the Periodic Table, the number of calculations becomes decidedly smaller. For argon, itself, electron-correlated values are to be found in Refs. [25], [45], [47], [55], [56] and [58]. The best values, CCSD(T), range from 11.07 to 11.17 au. 

For the chloride ion[25],[52],[58]-[60], there is a MP4 result of 38.01 and a CCSD(T) one of 37.43 au. The Pauling value, as for all anions, is an underestimate 24.7 au. For the K+ and Ca2+ anions, we appear to only have the density functional values in Ref. [54], these are 11.44 and 5.60 au, respectively. They are roughly twice the size of those in Table 1, but do agree with experimental results and it would seem that the Pauling approach is failing. 

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