A Comparison Model Between Density Functional and Wave Function Theories by Means of the Löwdin Partitioning Technique
A Comparison Model Between Density Functional and Wave Function Theories by Means of the Löwdin Partitioning Technique.
M. Caballero, I. de P. R. Moreira, J. M. Bofill
J. Chem. Phys., 138 (2013) 174107.
Representació qualitativa de la funció de Löwdin, f(E), per a un problema d’Interacció de Configuracions Total de dimensió 8 CSF i prenent H1,1 = EREF.
A comparison model based in the Löwdin partitioning technique is used to analyze the differences between the wave function and density functional models. It is argued that density functional theory can be compared to the wave-function theory using the Löwdin function, f(E), at E = 0. The density functional theory can be seen as a special case of Löwdin function that does not satisfy all variational conditions on r(r) and also on the EXC[r] term. This analysis shows that ignoring the restrictions imposed by the spin and space symmetry requirements the correlation expressed by the r(r) function will be inconsistent with a g1(r1;r1’) function derivable from a spin and space symmetry adapted wave function Y(r1s1,…,rnsn). The comparison scheme also provides a new insight on the variational requirements in order to achieve a consistent description of the molecular electronic structure of both ground and excited states. Some numerical results are reported.