The spin-flip equation-of-motion coupled-cluster electronic
structure method for a description of excited states, bond-breaking,
diradicals, and triradicals
A. I. Krylov
Acc. Chem. Res. 39, 83 – 91
The spin-flip approach to multi-reference situations
(e. g., bond-breaking, diradicals, and triradicals) is described.
Both closed and open shell low-spin states are described within a single
reference formalism as spin-flipping, e. g., α→β,
excitations from a high-spin reference state for which both dynamical and
non-dynamical correlation effects are much smaller than for the
corresponding low-spin state. Formally, the SF approach can be viewed as
an Equation-of-Motion model where target states are sought in the basis
of determinants conserving the total number of electrons but changing
the number of α- and β-electrons.
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