July 11, 2016

Modeling the effects of relativity on the excited states of atoms and molecules

Einstein's special relativity in known to measurably affect the time read by clocks on high speed jets, but it influences atomic clocks as well. Indeed, relativistic effects are ubiquitous in chemistry, bringing about the lustrous coloration of gold and the low melting point of mercury. Even more interestingly, relativity produces new magnetic interactions between the electrons' spin and their orbital motions.

In a new published work we have presented a novel approach to modeling relativistic effects on the electronic excited states of atoms and molecules, focusing on the splittings in the excited energy levels induced by spin-orbit couplings. We use a two-component approach of the wave function, modeled using the DKH and X2C methods, and include scalar and spin-orbit relativistic effects in the ground state variationally. We then compute excited state energies and transition densities by means of linear response theory. The strength of this approach is its computational efficiency, with a cost that is not significantly higher than a comparable non-relativistic calculation. As we demonstrated in a number of examples, the method is able to accurately reproduce the expected values with small deviations in many cases.