Relativistic bond contraction

AuH and Au2 serve as benchmark molecules to test the performance of various relativistic approximations. Figure 4.7 shows predictions for relativistic bond contractions of Au2 from various quantum chemical calculations over more than a decade. In the early years of relativistic quantum chemistry these predictions varied significantly (between 0.2 and 0.3 A), but as the methods and algorithms became more refined, and the computers more powerful, the relativistic bond contraction for Au2 converged and is now at 0.26 A. 

Figure4.7 Relativistic bond contractions A re for Au2 calculated in the years from 1989 to 2001 using different quantum chemical methods. Electron correlation effects Acte = te(corn) — /"e(HF) at the relativistic level are shown on the right hand side of each bar if available. From the left to the right in chronological order Hartree-Fock-Slater results from Ziegler et al. [147] AIMP coupled pair functional results from Stbmberg and Wahlgren [148] EC-ARPP results from Schwerdtfeger [5] EDA results from Haberlen and Rdsch [149] Dirac-Fock-Slater...

Figure 4.10 Calculated relativistic bond contractions ARte in A (circles and solid line, axis on the left-hand side) and relativistic change in the dissociation energy contractions (triangles and dashed line, axis on the right-hand side) for various diatomic compounds as a function ofthe electronegativity of the ligand.

Remarkably, the Hg—C bonds are shorter than the Cd—C bonds in the respective cyano-spinel 109 the probable reason is relativistic bond contraction with the Hg atom. 

Relativistic effects on calculated NMR shieldings and chemical shifts have sometimes been divided into "direct" and "indirect" effects. According to this point of view, indirect effects are those that result from relativistic changes of the molecular geometry (the well-known relativistic bond contraction (55) in particular) whereas direct effects refer to a fixed geometry. 

Relativistic Calculations on Metal Dimers and Metal Hydrides. Relativistic Bond Contraction and Relativistic Bond Stabilization... 

Hay et a/. ° have carried out effective potential calculations on AuH which yield the relativistic bond contraction of 0.26 A. The dissociation energy of AuH is increased by 0.5 eV as a result of relativistic contributions. They also presented calculations for AuCI, HgH and HgCl2- Ziegler, Snijders and Baerends have carried out perturbational relativistic calculations on a number of heteronuclear diatomics such as HgH, CdH", ZnH", AuH, AgH, CuH and CsH. 

On the Origin of Relativistic Bond Contraction. Chem. Phys. Lett., 75(1) (1980)... 

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