COMPACTNESS OF FULL CONFIGURATION INTERACTION WAVE FUNCTIONS: A SENIORITY NUMBER APPROACH

L. LAIN; A. TORRE; D.R. ALCOBA; G.E. MASSACCESI; O.B. OÑA

Galpagos

Congreso; CONGRESO DE QUÍMICOS TEÓRICOS DE EXPRESIÓN LATINA; 2014

Universidad de San Francisco - Quito

The concept of seniority number, widely used to classify Slater determinants1,2, is extended to wave functions of N electrons and spin S, as well as to N-electron spin-adapted Hilbert spaces. The formulation of the seniority number operator in terms of spin-free replacement operators3,4 allows us to determine the invariant character of its expectation value for spaces of N electrons and spin S and its non-invariant character for a determined wave function, under transformations of the molecular orbital basis sets. We study the convergence of the full configuración interaction wave function expansions in terms of Slater determinants using three types of basis sets: i) canonical molecular orbitals (CMO), ii) natural orbitals (NO), and iii) the orbitals which minimize the expectation value of the seniority number operator for that wave function (Mmin). The results show that the last expansions exhibit a superior convergence and that the expectation value of the seniority number operator provides a quantitative evaluation of the compactness of the wave functions5.1) C. C. J. Roothaan, J. Detrich, and D. G. Hopper, Int. J. Quantum Chem. 16, 93 (1979).(2) L. Bytautas, T. M. Henderson, C. A. Jiménez-Hoyos, J. K. Ellis, and G. E. Scuseria. J. Chem. Phys. 135, 044119 (2011). (3) A. Torre, L. Laín, and J. Millan, Phys. Rev. A 47, 923 (1993).(4) L. Lain and A. Torre, Phys Rev. A 52, 2446 (1995).(5) D. R. Alcoba, A. Torre, L. Lain, G. E. Massaccesi and O. B. Oña. J. Chem. Phys, 139, 084103 (2013).