We have tested the performance of a large set of kinetic energy density functionals of the local density approximation (LDA), the gradient expansion approximation (GEA), and the generalized gradient approximation (GGA) for the calculation of interaction energies within a subsystem approach to density functional theory. Our results have been obtained with a new implementation of interaction energies for frozen-density embedding into the Amsterdam Density Functional program. We present data for a representative sample of 39 intermolecular complexes and 15 transition metal coordination compounds with interaction energies spanning the range from -1 to -783 kcal/mol. This is the first time that kinetic energy functionals have been tested for such strong interaction energies as the ligand-metal bonds in the investigated coordination compounds. We confirm earlier work that GGA functionals offer an improvement over the LDA and are particularly well suited for weak interactions like hydrogen bonds. We do, however, not find a particular reason to prefer any of the GGA functionals over another. Functionals derived from the GEA in general perform worse for all of the weaker interactions and cannot be recommended. An unexpectedly good performance is found for the coordination compounds, in particular with the GEA-derived functionals. However, the presently available kinetic energy functionals cannot be applied in cases in which a density redistribution between the subsystems leads to strongly overlapping subsystem electron densities.
General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ?
Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
In this chapter we consider the extension of 4-component relativistic methods from atomic to molecular systems, in particular the chaIIenges arising from the introduction of the algebraic approximation. In order to analyze the variational stability of the relativistic many-electron Hamiltonian we derive a variational theory of QED in the semiclassicaI limit using the second quantization formalism and exponential parametrization. In QED the negative-energy orbitals are fiIIed leading to a true minimization principle for the electronic ground state, whereas in the standard 4-component approach these orbitals are empty and treated as an orthogonal complement, thus leading to a minimax principle. We emphasize the non-uniqueness of the resulting no-pair Hamiltonian of the standard approach. 4-component methods allow the continuous update of the Hamiltonian and thereby complete relaxation of the electronic wave function. We also discuss more practical aspects of the implementation of 4-component relativistic methods. We carefuIly analyze their computational cost and conclude that the difference with respect to non-relativistic methods constitute a prefactor and not a difference in order. We furthermore discuss how computational cost may be reduced while staying at the 4-component level, e.g. by exploiting the atomic nature of the small component density.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.