A theoretical study of the dissociation energy of Ni2+ A case of broken symmetry

✍ Scribed by Manuela Merchán; Rosendo Pou-Amérigo; Björn O. Roos

• Book ID: 103034168
• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 763 KB
• Volume: 252
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(96)00105-4

✦ Synopsis

The electronic structure and potential curves for the lowest states of the Ni~-cation have been studied using multiconfigurational SCF theory (CASSCF) combined with second-order perturbation theory (CASPT2) and non-orthogonal CI. The wavefunctions for the so-called or-hole states break symmetry at all internuclear distances longer than equilibrium. CASSCF and CASPT2 calculations were first performed using C2~ symmetry. Full symmetry was restored by mixing two symmetry related CASSCF wavefunctions. Ni~ has a 4E~-ground state with a computed bond energy of 2.47 eV and a bond distance of 2.19 .~. The approach leads to a somewhat large binding energy due to double counting of the resonance energy. An estimate of the error yields a binding energy of slightlay less than 2.4 eV. Calculations using D2h symmetry give a binding energy (D o) of 2.25 eV and a bond distance of 2.22 A, in apparent agreement with experiment (D o = 2.25 eV, r e = 2.22 ~,), indicating that the symmetry breaking error is independent of the internuclear distance.