CONFIGURATION INTERACTION WAVE FUNCTIONS: EXCITATION AND SENIORITY NUMBER BASED APPROACHES

DIEGO R. ALCOBA; ALICIA TORRE; LUIS LAIN; G. E. MASSACCESI; OFELIA B. OÑA; P. CAPUZZI; MARIO VAN RAEMDONCK; W. POELMANS; S. DE BAERDEMACKER; DIMITRI VAN NECK; PATRICK BULTINCK

Buenos AIres

Conferencia; MOLECULAR ELECTRONIC STRUCTURE BUENOS AIRES CONFERENCE (MESBA 2016); 2016

Instituto de Astronomía y Física del Espacio

Although the N-electron wave functions arising from the full configuration interaction (FCI) treatment are the exact solutions of the Schrödinger equation fora given basis set, their determination usually requires a great computational effort. To reduce this cost one formulates expansions of configurationinteraction (CI) in which only a limited number of N-electron Slater determinants is taken into account. The most popular criteria to select thesedeterminants are based on i) the particle-hole excitation level from a reference determinant and ii) the seniority number of the determinants1-3. In this workwe study the spin contamination of the CI N-electron wave functions provided by both approaches by means of the excitation operator and the senioritynumber operator, respectively. We show that the excitation based procedure leads to eigenfunctions of the spin squared operator if the excitations arecounted in terms of spatial orbitals while the seniority number based method always provides pure spin states4. Hybrid CI treatments5,6 based on bothseniority number and excitation schemes have also been investigated, showing its adequacy to describe systems which exhibit dynamic correlation atdetermined geometrical arrangements but show static correlation at other arrangements.