Theoretical studies of the dependence of nuclear quadrupole coupling constants on intermolecular forces

We study the performance of density functional methods in the calculation of nuclear quadrupole coupling constants (NQCCs), focusing on the effects of weak intermolecular forces. We begin with an analysis of isolated molecule values, comparing the density functional theory (DFT) results for uracil and thymine obtained by applying 11 different functionals with the Møller–Plesset second-order perturbation theory (MP2) values and with accurate experimental data. Next, using a subset of these DFT functionals we examine the interaction-induced changes of NQCCs for weak solute–solvent interactions, with the solvent effect described as a function of the dielectric constant; for adenine–thymine and guanine–cytosine complexes, in which we observe significant effects due to proton transfer in the hydrogen bonds, and for a hexamine complex in the solid state. Three applied DFT functionals provide a similar, satisfying description of the influence of intermolecular forces on the quadrupole coupling constants, in particular when hydrogen bonding leads to large changes of these constants.