Calculation of the diamagnetic component of the nuclear screening constant for C,N, O and F

‘Local’ and ‘nonlocal’ contributions to σ^d are calculated by INDO molecular orbital methods. It is demonstrated, by means of Pople's approach⁵ using ‘gauge dependent’ atomic orbitals, that σ is effectively constant for C, N, O or F in a number of chemically different environments and that σ is negligible. The use of Flygare's method¹² produces a significant and variable ‘nonlocal’ contribution, which renders σ^d in this formulation comparable to the gauge dependent term in Ramsey's expression.