Is the Use of Diffuse Functions Essential for the Properly Description of Noncovalent Interactions Involving Anions?

It is commonly assumed that theoretical DFT or ab initio calculations involving anions require the utilization of diffuse functions in order to obtain reliable results. In large systems, the use of diffuse functions in the calculations increases the computational cost and, more importantly, sometimes provokes self-consistent-field (SCF) convergence problems, especially in open shell systems. Nowadays, the popular and often used bases for studying noncovalent interactions are the correlation-consistent polarized basis sets of Dunning and co-workers, denoted as cc-pVXZ (X = D, T, etc.), and the Turbomole def2 basis set family (def2-SVP and def2-TZVP). In this paper we study the effect of the utilization of diffuse functions on the energetic and geometric features of several noncovalent complexes, including hydrogen, halogen, and pnicogen bonding, lithium bonds, anion−π interactions, and van der Waals interactions.