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Van An Du, G. Stipicic, U. Schubert:
"29Si NMR SHIELDING CALCULATIONS FOR HYPERVALENT SILICON COMPOUNDS";
Poster: 14. Österreichische Chemietage, Johannes Kepler Universität, Linz; 26.09.2011 - 29.09.2011; in: "14. Österreichische Chemietage - Program", (2011), Paper-Nr. PO-95, 1 S.

²⁹Si NMR chemical shifts of 14 tetra-, 10 penta- and 17 hexacoordinated silicon compounds were calculated employing density functional theory (DFT) using the gauge including atomic orbital (GIAO) formalism and compared to experimental values. The hybrid B3LYP functional, the GGA functional BPW91 and the meta-GGA functional HCTH407 were used in conjunction with the 6-31G(d,p) and the 6-311+G(2d) basis sets and a locally dense basis set [6-311G+(2d) on Si and 6-31G(d,p) on all other atoms]. The HCTH407/6-311+G(2d) level of theory consistently performed best with a mean average error (MAE) of 5.9 ppm between calculated and experimental chemical shift over the entire test set.
Overall, the choice of a suitable basis set exerted a much larger influence on the accuracy of the results than the choice of functional. Additional calculations for some outliers with the 6-311++G(2df,2pd) basis set yielded only small improvements while the economically attractive locally dense basis set yielded an MAE of 6.5 ppm with the HCTH407 functional over the entire test set after correction of systematic errors. For a smaller subset of the investigated molecules, GIAO-HF and MP2 ab initio calculations yielded better results than the DFT calculations (MAEs for HF, MP2 and HCTH407 were 3.9, 4.5 and 5.6 respectively) while requiring roughly two orders of magniture more CPU time.