Db. Chesnut, AN APPROXIMATE INFINITE-ORDER PERTURBATION-THEORY PRESCRIPTION FOR ISOTROPIC NMR CHEMICAL SHIELDINGS, Chemical physics letters, 246(3), 1995, pp. 235-238
Data in the literature from NMR chemical shielding calculations at Har
tree-Fock, MP2, MP3, and MP4 levels using large basis sets suggest tha
t the ratio of the various perturbation order contributions may be app
roximately constant with a value of -0.5. Under this assumption one ma
y sum the infinite perturbation series so that, with a knowledge of Ha
rtree-Fock and MP2 results, the infinite order shielding may be estima
ted. Applying this method to cited literature calculations provides NM
R shieldings that are as accurate as available MP4 and CCSD calculatio
ns and in good agreement with experiment.