Toward deformation densities for intramolecular interactions without radical reference states using the fragment, atom, localized, delocalized, and interatomic (FALDI) charge density decomposition scheme

A novel approach for calculating deformation densities is presented, which enables to calculate the deformation density resulting from a change between two chemical states, typically conformers, without the need for radical fragments. The Fragment, Atom, Localized, Delocalized, and Interatomic (FALDI) charge density decomposition scheme is introduced, which is applicable to static electron densities (FALDI-ED), conformational deformation densities (FALDI-DD) as well as orthodox fragment-based deformation densities. The formation of an intramolecular NH⋅⋅⋅N interaction in protonated ethylene diamine is used as a case study where the FALDI-based conformational deformation densities (with atomic or fragment resolution) are compared with an orthodox EDA-based approach. Atomic and fragment deformation densities revealed in real-space details that (i) pointed at the origin of density changes associated with the intramolecular H-bond formation and (ii) fully support the IUPAC H-bond representation. The FALDI scheme is equally applicable to intra- and intermolecular interactions.National Research Foundation of South Africa and University of Pretoria.http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1096-987X2018-05-15Chemistr

Assigning symmetry terms to molecular orbitals in asymmetric Fischer carbenes using FALDI in a theoretical study

Dissertation (MSc (Chemistry))--University of Pretoria, 2021.Molecular orbitals (MOs) are one of the most useful tools available for explaining and describing the electronic structure of a chemical system. These MOs are obtainable through different means, which falls under two approaches; the conceptual and computational approach. The conceptual approach is mostly limited to symmetric systems but provides a qualitative and interpretable result, this is obtainable through methods like Symmetry Adapted Linear Combinations (SALCs) of atomic orbitals. While the computational approach applies to any system, irrespective of the symmetry and provides quantitative results but is limited by the interpretability. In this study, a Fragment, Atomic, Localized, Delocalized, Interatomic (FALDI) electron density decomposition scheme-based approach is investigated that aims to bridge the conceptual and computational approach of MOs. Multiple distinct theoretical chemistry techniques have been used to produce a consistent and accurate model which labels MOs in asymmetric octahedral metal complexes. These techniques include the Quantum Theory of Atoms in Molecules (QTAIM) to obtain the atomic overlap matrix (AOM) which is used in FALDI to obtain electron density (ED). FALDI recovers the localized ED (loc-ED) and the delocalized ED (deloc-ED) which is needed for the FALDI MO analysis and FALDI fragments. The work illustrates how an asymmetric complex is manipulated into a symmetric function, which is used to obtain the symmetry terms. The symmetric functions are known as Natural Density Functions (NDFs) and is derived using the loc-ED of the metal centre. The relationship between the loc-ED and the deloc-ED can be correlated to recover the delocalized indices (DI) between two atoms interacting whilst assigning symmetry labels. The development of the model was tried and tested on a symmetric model system and a simple octahedral metal centred asymmetric system (Fischer carbene) to ensure consistency and validity. This study then took the FALDI MO analysis further and considered fragments. Fragments are a summation of diatomic interactions which allow multiple atoms interacting with each other to be considered. Linking the symmetry terms to the metal centre provides the delocalized interactions of the fragments, resulting in a quantitative tool that is also interpretable at a classical level. The result is a method that allows for bonding modes such as - and -character to be recovered while assigning contributions which can be traced back to each molecular orbital origin. The FALDI fragments were applied to multiple asymmetric Fischer carbene systems to not only further verify the robustness of the method but also to test the limits. Finally, experimental (with available data) Fischer carbene systems were considered for which novel interpretations and approaches were suggested, which promises a potential future in tuning Fischer carbene systems to achieve the desired chemical traits using the FALDI MO analysis technique.ChemistryMSc (Chemistry)Unrestricte

Comparison of DAFH and FALDI-like approaches

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.https://www.springer.com/journal/214hj2021Chemistr

Toward deformation densities for intramolecular interactions without radical reference states using the fragment, atom, localized, delocalized, and interatomic (FALDI) charge density decomposition scheme

A novel approach for calculating deformation densities is presented, which enables to calculate the deformation density resulting from a change between two chemical states, typically conformers, without the need for radical fragments. The Fragment, Atom, Localized, Delocalized, and Interatomic (FALDI) charge density decomposition scheme is introduced, which is applicable to static electron densities (FALDI-ED), conformational deformation densities (FALDI-DD) as well as orthodox fragment-based deformation densities. The formation of an intramolecular NH⋅⋅⋅N interaction in protonated ethylene diamine is used as a case study where the FALDI-based conformational deformation densities (with atomic or fragment resolution) are compared with an orthodox EDA-based approach. Atomic and fragment deformation densities revealed in real-space details that (i) pointed at the origin of density changes associated with the intramolecular H-bond formation and (ii) fully support the IUPAC H-bond representation. The FALDI scheme is equally applicable to intra- and intermolecular interactions.National Research Foundation of South Africa and University of Pretoria.http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1096-987X2018-05-15Chemistr