Distributed origin gauge

Yang D, Rauk A (1992) Vibrational circular dichroism intensities ab initio vibronic coupling theory using the distributed origin gauge. J Chem Phys 97 6517-6534... 

Locally Distributed Origin Gauge Calculations of Vbrational Circular Dichroism Intensity Formulation and Application to (S,S)-Oxirane-2,3-2H2. 

D. Yang and A. Rauk, J. Chem. Phys., 97,6517 (1992). Vibrational Circular Dichroism Ab Inido Vibronic Coupling Theory Using the Distribute Origin Gauge. 

Approximate models include the coupled oscillator (CO), the fixed partial charge (FPC), the chaige flow (CF), the ring current, the dynamic polarizability (DP), the bond dipole (BD), the localized molecular orbital (LMO) the nonlocalized molecular orbital (NMO), the atomic polar tensor (APT), and the locally distributed origins gauge... 

For atoms method (b) is successful. There is, in fact, a natural gauge origin at the position of the nucleus. For this choice 20 = 0 and 20 is evaluated rather easily. For molecules there is no natural gauge origin, but one should try to find something similar, as one does in the distributed gauge methods (see Section 4). 

The two most important methods for implementing distributed gauge origins are the GIAO and IGLO concepts. In the GIAO method one evaluates matrix elements of the Hamiltonian in terms of a basis of field-dependent atomic orbitals ... 

Recent CHF calculations with larger basis sets and distributed gauge origins suggest that Hartree-Fock results may still be reasonable for metal shifts of early transition metals in high formal oxidation states like Ti(IV) or Zr(IV) and, not too surprisingly, for d -systems (cf. examples in Ref. 1). Results on Mo shifts were much less satisfactory. For quantitative calculations of metal shifts in most transition metal compounds, the inclusion of electron correlation appears mandatory. 

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