Topology of Charge Density from Pseudopotential Density Functional Theory Calculations

The absence of core electrons in pseudopotential electronic structure calculations poses some important problems on determining the topology of density. The key feature of valence-only densities is the lack of critical points (CPs) at the nuclear positions affected by core removal, which are sometimes substituted by local minimum CPs, the substitution of a maximum by a minimum must be necessarily accompanied by the creation of other compensating CPs, including at least either one maximum or one ring CP. As density is relatively unaffected at distance points far enough the removed cores, these new CPs are expected to lie in the proximity of the latter, and the topology of density to closely resemble that of the AE density in the chemically relevant valence regions. This difficulty is well-known in literature, and several works have been devoted to elucidate how to bypass it (Cioslowski and Piskorz, 1996). The correct topologies may be obtained from core-reconstructed pseudo-AE densities. This paper will show how the correct topology can be obtained from pseudopotential calculations. In order to analyze the problems that arise from the core electrons, results obtained for Alanine (CH3CH (NH2) COOH), Aminophenol (C6H4 (OH) NH2), Ethene (C2H4), and Propanone ((CH3)2CO) using all-electron, pseudo-valence wavefunctions are reported. Keywords: Pseudopotential, core electrons, all-electron (AE) density, QTAIM, charge density topology