Calculation of NMR chemical shifts. VI. Gauge invariant and Hermitian condition.

A clear definition for the division of the magnetic shielding tensor (σ) into two terms of the diamagnetic part (σ d) and paramagnetic part (σ p) is proposed based on the gauge invariant coupled-Hartree–Fock (GI–CHF) theory. In this definition, both σ d and σ p are written individually by gauge invariant and Hermitian operators. The present formulas are applied to calculate the magnetic shielding tensors of diatomic molecules, and lead to better results, even with small basis sets, than gauge dependent results obtained with large basis sets. [ABSTRACT FROM AUTHOR]