Affiliations: [a] Dipartimento di Chimica, Università di Ferrara, via Borsari 46, I-44100 Ferrara, Italy | [b] Departamento de Quimica Fisica, Universidad de Sevilla – c/ Profesor Garcia Gonzalez, s/n. E-41012 Sevilla, Spain | [c] Laboratoire de Physique Quantique, UMR 5626, Université Paul Sabatier, 118, Route de Narbonne, 31062 Toulouse CEDEX, France
Note: [1] Also in Dipartimento di Chimica Fisica e Inorganica, Università di Bologna, Viale Risorgimento 4, I-40136 Bologna, Italy.
Abstract: Variational and Perturbative CAS-SCF-type algorithms based on molecular orbitals that preserve their physical nature during the iterative process are discussed. The methods are based on the iterative diagonalization of the one-body reduced density matrix. If localized guess orbitals are used, the locality property is kept by the final orbitals. The formalism can be used to reduce the number of active orbitals in CAS-SCF calculations on large systems, and in general to have a better control on the physical nature of the active space. The reduction from a complete to selected reference space is also possible in the case of Configuration-Interaction calculations.
Keywords: Ab-initio methods, local orbitals, CAS-SCF
