부산대학교 도서관

The bond nature in beryllium dimerhas been theoretically investigatedusing high-level ab initiomethods. A series of ANObasis sets of increasing quality, going from sp to spdf ghi contractions,has been employed, combined with HF, CAS-SCF, CISD, and MRCI calculationswith several different active spaces. The quality of these calculationshas been checked by comparing the results with valence Full-CI calculations,performed with the same basis sets. It is shown that two quasi-degeneratedpartly occupied orbitals play a crucial role to give a qualitativelycorrect description of the bond. Their nature is similar to that ofthe edge orbitals that give rise to the quasi-degenerated singlet–tripletstates in longer beryllium chains.1 [ABSTRACT FROM AUTHOR]