ab initio calculation 29si nmr chemical shift studies on silicate species in aqueous and gas phase

nowadays nmr spectroscopy becomes a powerful tool in chemistry because of the nmr chemical shifts. hartree–fock theory and the gauge-including atomic orbital (giao) methods are used in the calculation of 29si nmr chemical shifts of various silicate species in the silicate solution as initial components for zeolite synthesis both in gas and solution phase. calculations have been performed at geometries optimized at the am1 semi-empirical method. the giao-hf calculations were carried out with using different basis sets: 3-21g, 6-31g, 6-311g, 6-31g (d,p), 6-311g (d,p), 6-311g (2d,p) and 6-31g (2d,p). to demonstrate the quality of the calculations the calculated chemical shifts, δ, were compared with the corresponding experimental values for the compounds in study. the results, especially with 6-311g (2d, p) are in agreement with experimental values. also the calculated chemical shifts on gas phase have more agreement than solution phase.