Spin-orbit coupling diatomics

Computatation of Spin-Orbit Coupling Constants in Diatomic Molecules. 

To summarize, therefore, it is reasonable to say that ab initio calculations of spin-orbit coupling constants may be successfully performed on atoms (although relativistic wavefunctions will be necessary for the heavier ones) and diatomic molecules (especially hydrides). For larger molecules, such methods may be too time-consuming and resort to semi-empirical techniques will be necessary. The atoms-in-molecules approach has proved extremely successful, but it should be possible to use semi-empirical wavefunctions with the full hamiltonian before long. This will be probably more useful with very large molecules. 

Bussery-Honvault B, Moszynski R (2006) Ab initio potential energy curves, transition dipole moments, and spin-orbit coupling matrix elements for the first twenty states of the calcium diatom. Mol Phys 104 2387-2402... 

For the Tl, Pb, and Bi series of homonuclear diatomics, the impact of spin-orbit coupling decreases as electrons are added to the 6p shell. This is as one would expect in terms of the additional electrostatic interactions. 

Recently, Alexander et al [29] carried out an ab initio study of the four states (X A, A A", a A" and a A ) that correlate to OH-H in the product region and the electronic and spin-orbit couplings between them. These PESs were used to study the nonadiabatic effects on the branching between the product OH ( 77) multiplet levels, using a statistical model of atom-diatom insertion reactions combined with coupled-states capture theory. 

Liu, W. and van Wtillen, C. 1999. Spectroscopic constants of gold and eka-gold (element 111) diatomic compounds The importance of spin-orbit coupling. J Chem Phys 110, 3730-3735. 

Pitzer and coworkers have carried out relativistic calculations on a number of diatomics such as Xe2, Xcj, TIH, Au2, Auj, PbS, PbSe", etc. These calculations were carried out with an LCAS-MS (linear combination of atomic spinor—molecular spinor) approach with the relativistic effective potentials. Many of these calculations were at the level of single-configuration SCF. In the earlier calculations, the spin-orbit coupling was ignored at the SCF stage and introduced using a semi-empirical procedure. 

All the methods described above take into account electron-correlation effects but completely ignore spin-orbit coupling which is known to be very significant for molecules containing actinides and lanthanides. A method to introduce electron correlation and spin-orbit coupling for diatomics based on a SCF procedure was developed in 1982 by Christiansen et al. and was called the spin-orbit Cl (SOCI) method. This should be contrasted with the second-order Cl method which is also abbreviated as SOCI. In the spin-orbit Cl method which we prefer to call the relativistic Cl method, all electronic configurations which can mix in the presence of the spin-orbit operators are included variationally. However, this method was restricted to diatomics and only up to 5000 configurations could be included. 

Kotzian et al. (1991a, b) as well as Kotzian and Rosch (1991a, b) have applied the INDO/S-CI method extended to include spin-orbit coupling on the diatomic CeO. They have studied 16 electronic states of CeO arising from the 4f6s configuration of Ce" at the experimental of 1.820A. The results of their computations are shown in... 

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