High Cost-Effectiveness Ratio: GIAO-mPW1PW91/6-31G(d)//PM7 Scaling Factor for C-13 NMR Chemical Shifts Calculation

Abstract: In this paper, we present a GIAO-HDFT universal scaling factor and a linear regression comparative study, in which we intent to investigate the ability of GIAO-mPW1PW91/6-31G(d) using optimized geometries at the PM7 level of theory to achieve its high cost-effectiveness ratio. This level is computationally much less demanding than GIAO-B3PW91/cc-pVDZ//B3PW91/cc-pVDZ and GIAO-B3PW91/cc-pVTZ//B3PW91/cc-pVDZ, recently published for our research group. Despite the calculation approximations the chemical shifts calculated at the GIAO-mPW1PW91/6-31G(d)//PM7 using a simple relationship (delta(scal) = 1.06. delta(calc)-0.72, where delta(calc) and delta(scal) are the calculated and the linearly scaled values of the C-13 chemical shifts, respectively) were able to yield MAD and RMS errors as small as those obtained with other GIAO-HDFT (B3LYP, OPBE, B3PW91) with bigger basis sets, such as 6-311+G(2d,p) and cc-pVDZ and cc-pVTZ. Its high cost-effectiveness ratio scaling factor, as well as its successful applicability to practical problem, was confirmed. In conclusion, GIAO-mPW1PW91/6-31G(d)//PM7 linear regression obtained by using the experimental and the calculated data, is a very attractive tool as an alternative to more computationally demanding approaches, which are usually applied in order to achieve C-13 NMR chemical shift calculations.

Author(s): Costa, FLP; de Albuquerque, ACF; dos Santos, FM; de Amorim, MB

JOURNAL OF COMPUTATIONAL AND THEORETICAL NANOSCIENCE