DFT calculations are performed for oxo-cluster of transition metal which contain heavy atoms, I would like to know which one I have to take on consideration the spin orbit coupling or relativistic effects, and what is the difference between the both of them?
Thanks in advance.
SO-coupling is one of several relativistic corrections. The standard set of relativistic corrections for fine structure also involves the first order kinetic energy correction and the so-called Darwin term, see:
https://en.wikipedia.org/wiki/Fine_structure
Hi,
relativistic effects include relativistic kinetic energy correction, Darwin term and spin-orbit coupling. The sum of these terms is called fine structure (unfortunately some authors use fine structure in the same meaning with SO coupling).
Relativistic effects are calculated by solving Dirac equation. These are generally calculated as corrections to a previously completed nonrelativistic computation, such as DFT, etc. Molpro, Dirac, etc programs have suits which solve Dirac equation by performing Douglass-Kroll transformation (there exist many other ways too). These three terms may also be calculated perturbatively instead of solving Dirac equation.
For molecules including heavy atoms such as metals, it is sometimes easier to use ECP basis sets which include relativistic effects for inner shell electrons implicitly. For such large systems, performing a full (or direct) relativistic calculation is way difficult. I suggest performing a DFT calculation by using a mixed (and balanced) basis set including ECP.
Spin orbit term is due to the coupling between the orbital angular momentum of the electron with the spin angular momentum (which is considered to be due to the precession of the electron around itself). For states with non zero orbital momentum spin orbit calculations lead to a split of degenerated levels. relativistic corrections try to take in account the correction to the Hamiltonian when the kinetic energy of the electron is very large and thus relativistic. In general the relativistic effect can be neglected but in some rare cases its not negligible
In DFT there are three corrective terms to the Hamiltonian. For scalar-relativistic (SR) calculations, only the relativistic correction to the kinetic energy and the Darwin term are considered. When the correction due to spin-orbit coupling (SOC) is included, some call them fully relativistic calculations (SR+SOC).
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