The Klyachko conditions from the chemical viewpoint

Carlos Benavides-Riveros

Universidad de Zaragoza

e-mail: carlosbe@unizar.es

The Klyachko constraints on fermion occupation numbers have started to receive careful attention. In this talk we intend to report on three related aspects of direct chemical interest.

I. Numerical verification of pinned and quasi-pinned occupancy in realistic 3-electron atomic and molecular systems [Benavides-Riveros, Gracia-Bondia and Springborg, PRA 88, 022508 (2013); Benavides-Riveros and Springborg, forthcoming].

II. Pinning and quasi-pinning from the viewpoint of coupled cluster approximations to multi-electronic systems. 

III. "A pinned system is essentially a new physical entity, with its own dynamics and kinematics" (Klyachko). Thus the recent constructive solution by Mazziotti to the N-representability problem for 2-body density matrices [Mazziotti, PRL 108, 263002 (2013)], is likewise restricted.