Calculation of ²⁹Si Chemical Shifts Using a Density-Functional Based Tight-Binding Scheme

The shielding constants δ for ²⁹Si, and from it the chemical shifts δ, are calculated for a series of silicon compounds using the IGLO-DFTB method (Individual Gauge for Localized Orbitals, Density-Functional based Tight-Binding). The calculated values of silanes SinH2n+2 (n = 1-5), methylsilanes HnSi(CH3)4-n, and phenylsilanes HnSi(C6H5)4-n (n = 1-3), are compared with DFT calculations and experimental values. Geometries have been optimized using the DFTB method. Calculated geometries are in good agreement with experiment. Calculated chemical shifts correlate quite well with experimental values. After an empirical correction, the chemical shifts for silanes and methylsilanes obtained by DFTB are equivalent to those of DFT calculations. The rms errors with respect to experiment are 4.3 ppm for silanes, 6 ppm for methylsilanes and 6.8 ppm for phenylsilanes.