A DFT INVESTIGATION ON BASIS SET SIZE AND HYDROGEN-BONDING EFFECTS ON17OAND2HNQR PARAMETERS

Abstract

A systematic theoretical study on various maleic acid (MA) clusters has been carried out employing density functional theory (DFT) methods. The performance of two different functionals namely B3LYP and M06 in the prediction of geometries,17O and2H nuclei quadrupole coupling constant (CQ) values of the MA clusters has been assessed comparing the results to those experimental data. For DFT calculations, several basis sets have been used, including the recently developed Jensen's polarization-consistent basis set families, pcJ-n and pcS-n (n = 0,1,2,3). Calculations at the basis set limit indicate that the value of CQ(2H ) in monomer MA, changes by 0.01–0.04 kHz for each of the final two basis set increments, and seems reasonable to conclusion that the pcJ-3 result is within a few kHz of the basis set limit. Convergence with respect to basis set size was found to be very good, and the pcJ-1 and pcS-1 basis sets provided a good compromise between the basis set limit and computational expense. In most cases, the differences between B3LYP and M06 results for a given basis set are in a range of 1–2%. On the other hand, no systematic changes in the CQ(17O ) or CQ(2H ) were found for basis sets larger than double-ζ. Thus, the usual assumption that double-ζ basis set (pcJ-1 and pcS-1) results in the acceptable CQvalues, seems to be valid in the case of17O and2H nuclei.