Spin–orbit corrections to NMR shielding constants from density functional theory. How important are the two-electron terms?

Ž . Ž . A recently developed density functional theory DFT ansatz for the calculation of one-electron spin–orbit SO corrections to NMR chemical shifts has been extended to include two-electron SO operators. The performance of different approximations is evaluated in calculations of H and C nuclear shieldings in the hydrogen halides, the halomethanes, and in iodobenzene. Two-electron contributions are significant relative to the one-electron contributions for fluorine substituents Ž . Ž . ca. 30–35% but decrease for the heavier halogens ca. 6–7% for iodine . A mean-field approximation to the two-electron SO integrals performs excellently, with negligible deviations from the ‘exact’ results, thus opening the way to calculations on large systems. q 1998 Elsevier Science B.V. All rights reserved.