Desclaux code

The analysis of the results obtained showed the relevance of the inner shell polarization which was accounted for by the UHF calculations. Since a fully numerical four-component code including exchange was not at hand at that time the authors also had to analyze the impact of Slater s exchange approximation especially its transferability from the nonrelativistic to the relativistic realm. Shortly after these investigations Desclaux and Bessis presented fully numerical four-component calculations now substituting Slater s approximation by an explicit treatment of exchange and reported results for A and B values of Sc, Cu, Ga and Br [79]. 

P. IndeRcato, E. lindroth, J. P. Desclaux. Nonrelativistic limit of Dirac-Fock codes The role of BriHouin configurations. Phys. Reo. Lett, 94 (2005) 013002. 

A practical instrument for many-electron open shell system is still the MCDF method. There are several modifications of it implemented into computational codes of Desclaux [57], developed further by Indelicato [36], of Grant [58] and Frose-Fisher [59]. Based on the Cl technique, the MCDF method accounts for most of the correlation effects while retaining a relatively small number of configurations. It can treat a large number of open shell configurations and can be applied to elements with any number of valence electrons. It omits, however, dynamic correlation, since excitations of the type (nj) n j) cannot be handled, and some core polarization, which makes it less accurate than the DC(B) CC methods. An average error for IP of heavy elements is about 1 eV. Calculations for many heaviest and superheavy elements were performed with the use of the AL version [23-31], as well as with a more accurate OL one [36]. 

Desclaux has developed a numerical Dirac-Fock code for atoms which can be used to obtain relativistic numerical allelectron four-component spinor wavefunctions for any atom in the periodic table. The relativistic four-component wave-functions for all the atomic orbitals could then be used for the construction of pseudo-orbitals and relativistic effective core potentials. The resulting relativistic potentials would also have four component spinor forms. 

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