Modelling the electronic structure of intermetalloid cluster compounds

Thesis

Intermetalloid clusters consist of a number of transition metal atoms surrounded by a larger number of p-block metal/metalloid atoms. The clusters are notable for how their transition metal and p-block units influence each other’s structures, which frequently leads to novel bonding and structures in the two units. To understand the properties of intermetalloid clusters, bonding models are frequently employed. Existing bonding models explain a large number of intermetalloid clusters, though there are also compounds which do not conform well to existing models. Additionally, the current understanding of what causes an intermetalloid cluster to adhere to a particular bonding model is limited. As such, the bonding models of intermetalloid clusters are an active area of research. Furthermore, electronic structure methods are often used to gain insight into intermetalloid clusters from a theoretical standpoint. However, the clusters can push the limits of existing electronic structure methods, thereby presenting a need to develop methodologies using electronic structure methods to allow for accurate modelling of the properties of intermetalloid clusters.

This thesis presents contributions to both the development of bonding models for intermetalloid clusters and to the development of electronic structure methodologies suited to intermetalloid clusters. The first two chapters provide an introduction to the fields of electronic structure methods and intermetalloid clusters, as well as a review of the theoretical background underpinning the methods used in the thesis. Chapter three then presents a characterisation of the electronic structure of the newly synthesised [Cr6Sn8Sb8 (en)2 ] 3–. It is argued that the compound can be described in terms of an existing bonding model which could not be applied to previously observed Cr6 clusters. Chapter four develops an electronic structure methodology aiming to establish the global minima of two isoelectronic intermetalloid clusters: Cr@Si14 and [Mn@Si14] + . Doing so provides insight into the conditions under which M@Si14 compounds adopt structures described by different bonding models. Lastly, with the goal of increasing the proportion of the correlation energy of core electrons that may be calculated for intermetalloid clusters, expressions for correlation-induced core orbital relaxation are derived within the Brueckner coupled-cluster theoretical framework as an alternative to the frozen core approximation. While it is found that the core orbital relaxation only captures a small portion of the core correlation energy, the investigation highlights how the core orbital relaxation is affected by double excitations, which has further implications for the development of approximations for core correlation in coupled-cluster methods.

Authors: Manley, A

• DOI: 10.5287/ora-w4ym9wzm4
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Subjects: Chemistry, Physical and theoretical; Chemistry, Inorganic