Comparison of DAFH and FALDI-like approaches
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Comparison of DAFH and FALDI‑like approaches David L. Cooper1 · Jurgens H. de Lange2 · Robert Ponec3 Received: 30 June 2020 / Accepted: 6 October 2020 © The Author(s) 2020
Abstract Two complementary methodologies for extracting useful insights into electronic structure and bonding from contemporary wavefunctions are compared. The first of these, known as the analysis of domain-averaged Fermi holes (DAFH), mostly provides visually appealing descriptions of the role and the extent of electron sharing in chemical bonding. The second one, known as the fragment, atom, localized, delocalized and interatomic (FALDI) charge density decomposition scheme, uses the partitioning of certain localization and delocalization indices to focus on highly visual contributions associated with individual domains and with pairs of domains, respectively. Four variants of a FALDI-like approach are investigated here in some detail, mostly to establish which of them are the most reliable and the most informative. In addition to ‘full’ calculations that use the correlated pair density, the consequences for the DAFH and FALDI-like procedures of using instead a popular one-electron approximation are explored. Additionally, the geometry dependence of the degree of acceptability of the errors that this introduces for delocalization indices is assessed for different formal bond multiplicities. The familiar molecular test systems employed for these various linked investigations are the breaking of the bonds in H2 and in N2, as well as the nature of the bonding in B2H6, as a simple example of multicenter bonding. One of the key outcomes of this study is a clear understanding of how DAFH analysis and a particular variant of FALDI-like analysis could be most profitably deployed to extract complementary insights into more complex and/or controversial bonding situations. Keywords Fragment, atom, localized, delocalized and interatomic (FALDI) charge density decomposition · Domainaveraged Fermi hole (DAFH) analysis · Shared-electron distribution index (SEDI) · One-electron approximation · Pair density
1 Introduction
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00214-020-02686-w) contains supplementary material, which is available to authorized users. * David L. Cooper [email protected] * Jurgens H. de Lange [email protected] * Robert Ponec [email protected] 1
Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, UK
2
Theoretical Chemistry, Department of Chemistry, Faculty of Natural and Agricultural Sciences, University of Pretoria, Gauteng, South Africa
3
Institute of Chemical Process Fundamentals, Czech Academy of Sciences, Suchdol 2, 165 02 Prague 6, Czech Republic
Advances in understanding electronic structure and bonding continue to rely not only upon the development and application of computational strategies for carrying out accurate calculations, but also upon the development and application of reliable techniques for extracting u
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