title: Full Configuration-Interaction Study on the Tetrahedral Li4 Cluster.
abstract: The Li4 cluster low lying electronic states were studied. In particular we investigated the tetrahedral geometry at full CI and coupled cluster level, with basis sets of increasing quality. The (5)A2 electronic state, characterized by having all the valence electrons unpaired, forming a quite stable no-pair bonding state, was studied in greater detail. In order to compare the energies we also studied the Li4 rhombus singlet ground state. The ability of coupled cluster with perturbative triples to correctly reproduce energy levels in a quasi-degenerate system was validated with respect to the full CI.
authors.affiliation: Dipartimento di Chimica Fisica e Inorganica, Università di Bologna, Viale Risorgimento 4, I-40136 Bologna, Italy, Instituto de Ciencia Molecular, Universitat de Valencia, Edificio de Institutos, Campus de Paterna 46980, Valencia, Spain, and Laboratoire de Chimie et Physique Quantiques, Université de Toulouse et CNRS, 118, Route de Narbonne, F-31062 Toulouse CEDEX, France.
authors.forename: Antonio
authors.initials: A
authors.lastname: Monari
authors.affiliation: Dipartimento di Chimica Fisica e Inorganica, Università di Bologna, Viale Risorgimento 4, I-40136 Bologna, Italy, Instituto de Ciencia Molecular, Universitat de Valencia, Edificio de Institutos, Campus de Paterna 46980, Valencia, Spain, and Laboratoire de Chimie et Physique Quantiques, Université de Toulouse et CNRS, 118, Route de Narbonne, F-31062 Toulouse CEDEX, France.
authors.forename: Jose
authors.initials: J
authors.lastname: Pitarch-Ruiz
authors.affiliation: Dipartimento di Chimica Fisica e Inorganica, Università di Bologna, Viale Risorgimento 4, I-40136 Bologna, Italy, Instituto de Ciencia Molecular, Universitat de Valencia, Edificio de Institutos, Campus de Paterna 46980, Valencia, Spain, and Laboratoire de Chimie et Physique Quantiques, Université de Toulouse et CNRS, 118, Route de Narbonne, F-31062 Toulouse CEDEX, France.
authors.forename: Gian Luigi
authors.initials: GL
authors.lastname: Bendazzoli
authors.affiliation: Dipartimento di Chimica Fisica e Inorganica, Università di Bologna, Viale Risorgimento 4, I-40136 Bologna, Italy, Instituto de Ciencia Molecular, Universitat de Valencia, Edificio de Institutos, Campus de Paterna 46980, Valencia, Spain, and Laboratoire de Chimie et Physique Quantiques, Université de Toulouse et CNRS, 118, Route de Narbonne, F-31062 Toulouse CEDEX, France.
authors.forename: Stefano
authors.initials: S
authors.lastname: Evangelisti
authors.affiliation: Dipartimento di Chimica Fisica e Inorganica, Università di Bologna, Viale Risorgimento 4, I-40136 Bologna, Italy, Instituto de Ciencia Molecular, Universitat de Valencia, Edificio de Institutos, Campus de Paterna 46980, Valencia, Spain, and Laboratoire de Chimie et Physique Quantiques, Université de Toulouse et CNRS, 118, Route de Narbonne, F-31062 Toulouse CEDEX, France.
authors.forename: Jose
authors.initials: J
authors.lastname: Sanchez-Marin