Gauge-including atomic orbital approach

Allouche et alP calculated chemical shifts (5 values) and SSCCs (/values) for the putrescine molecule, a polyamine present in prostate tissue, using a B3LYP-DFT/6-311-I-- -G(/,/))/PCM/GIAO (gauge-including atomic orbital) approach. From the computed and J values, the H NMR spectrum of putrescine was simulated. Comparisons between the calculated and the experimental NMR spectra at 400 MHz showed a good agreement and allowed to propose reliable values for the NMR spin Hamiltonian parameters of putrescine to be used for further development of quantitative analytical methods of metabolites in prostate tissue. 

The gauge origin dependence of this term, arising from the angular momentum 1 (i) of the ith electron, can be effectively treated by the so-called Gauge Including Atomic Orbital (GIAO) approach [21,22],... 

Another theoretical method, extensively exploited in chemical shift shielding calculation is gauge-including atomic orbitals (GIAO) [177] approach. That technique provides reasonable chemical shifts values for various nuclei. It should be noted that this approach does not take into account the periodicity of the crystal lattice and calculations are carried out for isolated molecules (gas phase). If analysis of intermolecular interactions is target of the project or there is its important part, then arbitrarily constructed cluster model has to be built up. 

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