摘要
Chemical shifts σ have been calculated by EHMO, INDO, MINDO, Fenske-Hall and X. methods, which are able to account for the experimental trends generally. The main difficulty is due to the uncertainty of the orbital energy.To overcome this difficulty, the eigenfunction and eigenvalue should be obtained by the ab initio method, using the gauge invariant atomic orbitals and the approximations of neglecting overlap for calculation.
