A new class of chemical bonds

Shason Shaik and collaborators have a nice article in the latest Nature Chemistry, "charge-shift" bonding which is the essential component of the bonding of pairs of very electronegative identical atoms (e.g., flourine).

The essential physics of covalent bonding can be described by a two-site Hubbard model (with U>>t).

Can a negative U (or V>U) two-site Hubbard model describe the essential physics of charge-shift bonding?

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