The triplet instability of closed-shell molecules was analyzed. From the point of view of orbital stability and occupation numbers of the charge density matrix, the problem which gives rise to pronounced spin contamination was analyzed. The onset, rather than the magnitude of the spin contamination was studied in detail for diatomics. It was shown that calculations of equilibrium molecular properties using coupled-cluster methods based on unrestricted Hartree-Fock reference should be monitored carefully for any molecule containing a multiple bond, especially when the bonded pair of atoms appear in different rows of the periodic table.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry