Ab initio calculations of 29Si solid state NMR chemical shifts of silane and silanol groups in silica

We report the results of first principles density functional theory (DFT) calculations on the 1H and 29Si NMR chemical shifts of silane and hydroxyl groups in silica. The structure of the isolated ≡Si–H and ≡Si–OH or of the geminal =Si(H)2 and =Si(OH)2 defects has been fully optimized from mechanically embedded cluster models derived from crystalline α-quartz and the nuclear magnetic shielding properties have been determined according to the GIAO method. The computed 29Si chemical shifts, δ(29Si) in ppm, are (in parenthesis the experimental values): ≡Si–OH −99 (−99), ≡Si–H −86 (−85), =Si(OH)2 −85 (−89), =Si–(H)2 −55 (−50).