Spin-orbit coupling energy parameters

There is a nice point as to what we mean by the experimental energy. All the calculations so far have been based on non-relativistic quantum mechanics. A measure of the importance of relativistic effects for a given atom is afforded by its spin-orbit coupling parameter. This parameter can be easily determined from spectroscopic studies, and it is certainly not zero for first-row atoms. We should strictly compare the HF limit to an experimental energy that refers to a non-relativistic molecule. This is a moot point we can neither calculate molecular energies at the HF limit, nor can we easily make measurements that allow for these relativistic effects. 

Fig. 2. Temperature dependence of the HS fraction % according to the Ising model. The employed parameter values are = 150 K, Aj = Aj = 500 cm and X = — 100 em h Here, Aj and Aj are the orbital energy differences between the and levels and between the Bj and levels, respectively, X being the spin-orbit coupling constant. The model parameters A, Aj, and X determine the value of AG. The levels result from the HS iron(II) ground state in orthorhombic symmetry according to Bj -1- B2 + B. The figures on the curves specify the values of...

Figure 5. Low-energy vibronic spectrum in a 3 A electronic state of a linear triatomic molecule. The parameter c determines the magnitude of splitting of adiabatic bending potential curves, As0 is the spin-orbit coupling constant, which is assumed to be positive. The zero on the...

In simple crystal field theory, the electronic transitions are considered to be occurring between the two groups of d orbitals of different energy. We have already alluded to the fact that when more than one electron is present in the d orbitals, it is necessary to take into account the spin-orbit coupling of the electrons. In ligand field theory, these effects are taken into account, as are the parameters that represent interelectronic repulsion. In fact, the next chapter will deal extensively with these factors. 

For all results in this paper, spin-orbit coupling corrections have been added to open-shell calculations from a compendium given elsewhere I0) we note that this consistent treatment sometimes differs from the original methods employed by other workers, e.g., standard G3 calculations include spin-orbit contributions only for atoms. In the SAC and MCCM calculations presented here, core correlation energy and relativistic effects are not explicitly included but are implicit in the parameters (i.e., we use parameters called versions 2s and 3s in the notation of previous papers 11,16,18)). 

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