Embedded density functional approach for calculations of adsorption on ionic crystals

Abstract

We present an embedded density functional approach to study adsorption on crystalline surfaces. Following ideas suggested by Cortona, Wesolowski, and Warshel, we divide the total system into a quantum cluster and the surrounding lattice whose density is assumed to be the same as in the ideal crystal. In this case the Kohn-Sham Hamiltonian for electrons in the cluster contains additional terms corresponding to the Coulomb, exchange, correlation, and ''nonadditive kinetic energy'' potentials from the environment. Test calculations for the He and Ar dimers, X-H 2 O molecular complexes ͑XϭLi ϩ , Na ϩ , K ϩ , F Ϫ or Cl Ϫ ͒ and water adsorption on the ͑001͒ surface of the NaCl crystal suggest that this model provides a promising alternative for cluster models employed earlier for calculations of defects and adsorption on ionic crystals.

Accurate basis set truncation for wavefunction embedding

“…ding calculation allows for the improper transfer of electron density from the embedded subsystem to the surrounding environment. [51][52][53] As we show in Sec. III C, this problem can be remedied in the context of truncated projection-based embedding.…”

On the electron leak problem in orbital-free embedding calculations

“…We can conclude, therefore, that there is no need to modify ad hoc the general KSCED framework by including pseudopotentials representing core electrons as proposed, for instance, in Ref. 8-at least for the case of the studied charged complexes: F − H 2 O for which an erroneous behavior of the potential energy curve was reported 8 previously and for Li + H 2 O which was used as a case where the collapse of the electron density on the cation could be expected to result from flaws in the repulsive part of the embedding effective potential.…”

“…1 Ref. 8 occurs even for molecular distances as short as 1.0 Å. Figure 2 shows the electron density perturbation ⌬ ͑de-fined as the difference between the total electron density obtained from either the KSCED or Kohn-Sham methods and the sum of densities of isolated subsystems calculated using the Kohn-Sham method͒ obtained from KSCED͑s͒, KSCED͑m͒, and Kohn-Sham calculations for F − H 2 O at d͑F-H͒ = 1.3 Å distance.…”

“…In Ref. 8, it was argued that this divergence is the cause of the artificial attraction between the F − anion and the H 2 O molecule at short intermolecular separations. This erroneous result can be attributed to the approximations to the functional or/and functional derivative of the nonadditive kinetic energy, choice of B , the divergence of the KSCED embedding potential, or last but not least flaws in the numerical implementation of the KSCED formalism.…”

“…͑3͒ form in computer simulations of condensed matter systems. 3,[8][9][10][11][12][13] To this end, two model systems for which the flaws of the KSCED effective embedding potential can be expected are analyzed: the F − H 2 O complex which is formally divided into two subsystems each comprising ten electrons and the Li + H 2 O complex partitioned into subsystems containing two and ten electrons. The existence of the infinitely deep hole in the embedding potential should result in some intersubsystem charge transfer in either cases.…”