Gauge-Independent Atomic Orbital

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. 

GIAO method (Gauge Independent Atomic Orbitals), 126... 

Gauge-independent atomic orbitals. GlAOs are eigenfunctions of a one-electron system that have been perturbed by an external magnetic field. 

The structure of a natural product hexacyclinol, a polycyclic endoperoxide, was reassigned on the basis of calculated chemical shifts (HF-gauge-independent atomic orbital (GIAO) level of theory) <2006OL2895>. 

K. Wolinski, J. F. Hinton and P. Pulay, Efficient implementation of the gauge-independent atomic orbital method for NMR chemical-shift calculations. J. Am. Chem. Soc., 1990, 112,8251-8260. 

Computational Details. Restricted Hartree-Fock (RHF) calculations were carried out using Gaussian 94 (45) and ACES II (46) on an IBM RISC/6000 computer. The gauge independent atomic orbitals (GIAO) method was used for the shielding calculations (47). All second-order many-body perturbation theory (MBPT2, also referred to as MP2) calculations were performed with ACES II (46). 

NMR shielding tensors were calculated using the Gauge-Independent Atomic Orbital (GIAO) method as implemented in Gaussian 98 (44-46). The basis sets and level of theory are the same as used in the geometry optimizations and frequency calculations mentioned above. 

Most recently, ab initio calculations for the NMR chemical shifts have become available for medium-size molecules because of the remarkable power capabilities of modernworkstations, personal computers and supercomputers [32]. This leads to a quantitative discussion on the chemical shift behaviors. For example, the ab initio MO calculation with the 4-31G basis set using the GIAO-CHF (gauge independent atomic orbital-coupled Har-tree-Fock) method on A-acetyl-A -methyl-L-alanineamide which is the same model molecule as the case of the above FPT INDO calculation will be... 

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