An empirical charge transfer potential with correct dissociation limits

Abstract

The empirical valence bond (EVB) method [J. Chem. Phys. 52, 1262Phys. 52, (1970] has always embodied charge transfer processes. The mechanism of that behavior is examined here and recast for use as a new empirical potential energy surface for large-scale simulations. A two-state model is explored. The main features of the model are: (1) Explicit decomposition of the total system electron density is invoked; (2) The charge is defined through the density decomposition into constituent contributions; (3) The charge transfer behavior is controlled through the resonance energy matrix elements which cannot be ignored; and (4) A reference-state approach, similar in spirit to the EVB method, is used to define the resonance state energy contributions in terms of "knowable" quantities. With equal validity, the new potential energy can be expressed as a nonthermal ensemble average with a nonlinear but analytical charge dependence in the occupation number. Dissociation to neutral species for a gas-phase process is preserved. A variant of constrained search density functional theory is advocated as the preferred way to define an energy for a given charge.PACS numbers: 71.15.-m, 34.70.+e, 34.20.-b, 31.15.-p

First principles approach to ionicity of fragments

“…Along the direction of descriptors of the states of atoms, the recently developed FH model [24][25][26][27], based on Moffitt's atomsin-molecules (AIM) form of the many-electron Hamiltonian operator [30][31][32][33][34], puts forward a new perspective on ionicity as a variable paired with ''fragment hardness''. Within the broad framework of the FH model, a system can be expressed as a collection of fragments and the identity of the fragments can be defined as any collection of nuclei and electrons.…”

“…Within the FH model [24][25][26][27], a trial state for an overall neutral diatomic molecule AB can be defined based on the allowed integer charge states of A and B as follows [23,35,36] jABi…”

“…Recently though, such a concept of ionicity for fragments was advanced within the Fragment Hamiltonian (FH) approach, closely following Mulliken's approach to electronegativity [24][25][26][27]. Fragment ionicity could be defined as an occupation number that is paired, in the sense of conjugate variables, with the chemical hardness of Parr and Pearson [28], in a manner analogous to how particle number and Mulliken electronegativity are conjugate pairs [29].…”

ACKS2: Atom-condensed Kohn-Sham DFT approximated to second order

“…47 One can also suppress the impact of electronegativity differences at long distances. 59,63,64 A promising strategy to obtain correct dissociation limits, is the derivation of EEM variants from valence bond theory, 59,[63][64][65] but to our knowledge no one has yet shown the transferability of parameters in these models within a broad class of molecular systems.…”

Simulating Interface Growth and Defect Generation in CZT – Simulation State of the Art and Known Gaps

“…One of the early successful attempts to include many-body effects was the introduction of the embedding functional [235], which depends on nonlinearly upon the coordination number of each atom. This development leads to the birth of the embedded atom method (EAM) [236,237], which provides relatively accurate description of noble transition metals and their alloys, Tersoff potential formulism [238], which is based on the concept of bond order and has been applied to a large number of semiconductors, and Buckingham potential [239] or charge transfer potentials [240,241] for oxides.…”