Relativistic Methods for Molecular Calculations and Diatomic Gold Compounds

Relativistic Methods for Molecular Calculations and Diatomic Gold Compounds 

We briefly discuss the performance of the relativisitic pseudopotential approximation with respect to all-electron methods, as this is the most widely used relativistic 

CCSD(T) calculations predict a relativistic increase in the dissociation energy of 78kJmol [155]. In comparison, electron correlation increases the dissociation energy by 134kJ mol . Spin-orbit effects increase the dissociation energy further by about 3kJmol [158]. Thus we predict a ArDe value of about SOkJmol. A comparison of calculated force constants reveals a similar picture, see Ref. [131]. 

To summarize, the RPPA is a method that can accurately describe relativistic effects, even though the relativistic perturbation operator used in the pseudopotential procedure is acting on the valence space and not the region dose to the nudeus, as this is the case for the correct all-electron relativistic perturbation operator. That is, relativistic effects are completely transferred into the valence space. These effects are also completely transferable from the atomic to the molecular case as the results for Au2 show. If relativistic pseudopotentials are carefully adjusted, they can produce results with errors much smaller than the errors originating from basis set incompleteness, basis set superposition or from the electron correlation procedure applied. 

The error inherent in the RPPA is certainly much smaller than the many approximations used in DPT. 

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