GIAO

The most reliable results are obtained using ah initio methods with moderate-to large-sized polarized basis sets. The use of gauge-independent atomic orbitals (GIAO) removes gauge dependency problems. 

London (1937) first made use of these functions in connection with ring cun-ents in aromatic hydrocarbons. A key paper for the use of GIAO is that of Ditch-field. 

While LAO/GIAO had been proposed well before the advent of modem computational chemistry, it was only developments in calculating (geometrical) derivatives of the energy (and wave function) that made it practical to use field-dependent orbitals. ... 

The nitrogen NMR shieldings in methylated triazoles and tetrazoles were computed at the GIAO/HF/6-31-I--I-G level and more recently using multireference... 

Fock limit. It has also been pointed out by Wolinski et al. [14] that the use of GIAO s permits to reduce the basis set dimension when evaluating screening constants. All the details of the method of calculation are given in references [15-19], so they will not repeated here. 

The following computations supported the existence of MesjSi as a free cation lacking observable coordination to solvent and having a calculated value of the Si NMR chemical shift very close to the experimental value 230.1 (GIAO/HF) and 243.9 (GlAO/DFT)ppm versus 225.5ppm. ... 

Alkorta, I., Elguero, J., 1998, Ab Initio Hybrid DFT-GIAO Calculations of the Shielding Produced by Carbon-Carbon Bonds and Aromatic Rings in H NMR Spectroscopy , New J. Chem., 381. 

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