Fermi-Amaldi approximation

The shape function had a role in theoretical chemistry and physics long before it was named by Parr and Bartolotti. For example, in x-ray measurements of the electron density, what one actually measures is the shape function—the relative abundance of electrons at different locations in the molecule. Determining the actual electron density requires calibration to a standard with known electron density. On the theoretical side, the shape function appears early in the history of Thomas-Fermi theory. For example, the Majorana-Fermi-Amaldi approximation to the exchange potential is just [3,4]... 

The exchange and correlation contributions must be approximated, but acceptably accurate models were available even in the 1930s (e.g., the Fermi-Amaldi model and the Dirac model for exchange - and the Wigner model for correlation ). 

Density functionals which are not size consistent are to be avoided. An example is the Fermi-Amaldi [48] approximation for the exchange energy,... 

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See also in sourсe #XX -- [ , ]

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