Readdressing molecular dissociation within the Kohn–Sham formalism of density-functional theory: simple models and a different point of view

Abstract

Within the Kohn–Sham (KS) formalism of density-functional theory (DFT), most available exchange-correlation (XC) density-functionals are known to yield incorrect molecular dissociation even when dealing with simple molecules as H. It is known that the KS potential must develop a peak and a step in the region between the isolated atoms, in order to prevent electrons to hop from one atom to another, and hence avoiding fractionally charged dissociated atoms. Considering one-dimensional models of two-electron homo and heteronuclear molecules, we here (i) readdress the limit of dissociated molecules, with a different point of view on the formation of the peaks and steps in the KS potential and (ii) investigate a simple approach to treat not necessarily dissociated molecules, by employing single-particle orbitals (not KS orbitals). Our results indicate that an accurate description of dissociation can be achieved.