Performance of B3PW91, PBE1PBE and OPBE Functionals in Comparison to B3LYP for 13C NMR Chemical Shift Calculations

Abstract

The performance of density functionals B3PW91, PBE1PBE and OPBE are evaluated in comparison to the B3LYP for the ¹³C NMR chemical shift calculations of 20 small molecules. We combine these functionals with several basis sets including 6-311++G(d,p), 6-311++G(2d,2p), 6-311++G(3df,3pd) and cc-PVTZ to analyze the effect on predicting ¹³C NMR chemical shifts. Our computed results show that the use of a simple expression 𝛿𝑠𝑐𝑎𝑙=0.9528𝛿𝑐𝑎𝑙𝑐−0.5986, where 𝛿𝑐𝑎𝑙𝑐 and 𝛿𝑠𝑐𝑎𝑙 are the calculated and the linearly scaled values of the ¹³C chemical shifts, respectively, significantly improves the mean absolute deviations for a set of 75 chemical shifts considered. In addition the B3PW91 is superior to the other three density functionals and the GIAO B3PW91/6-311++G(2d,2p) is sufficient to determine accurate ¹³C chemical shifts. The ¹³C NMR chemical shifts of a larger system, i.e. Taxol molecule, are also computed and compared with experimental values.