Eduard Matito

Electron delocalization error is one of the most pervasive deficiencies of modern density-functional approximations (DFAs). It leads to an inaccurate description of molecular electron distributions and, in turn, to a severe overestimation of electron delocalization and aromaticity. These effects can be mitigated by employing DFAs with a sufficiently large fraction of Hartree–Fock exchange (HFX). Yet, despite extensive analyses of this problem, the literature still contains routine studies of molecules prone to delocalization errors that rely entirely on functionals such as B3LYP. Other works adopt an intermediate strategy, evaluating properties with a DFA less susceptible to delocalization error but using geometries optimized with functionals containing low HFX. In this work, we analyze the extent to which delocalization error affects molecular geometry and electronic properties, and how these two effects become intertwined, leading to a spurious description of chemical bonding. By examining delocalization and aromaticity descriptors of different nature, we identify which combinations of geometries and property-evaluation functionals, as well as which classes of molecules, are most prone to large delocalization errors. Our results also show how these errors can be substantially minimized through a judicious choice of DFA.