Theory and modelling of electron transport in molecular-scale condensed matter

Studying electron transport properties in molecular junctions, comprising a molecule as the scattering region coupled to metallic electrodes is critical for nano- and molecular-scale applications. This thesis focuses on the thermoelectric properties of a specific type of two-terminal molecular junction involving gold electrodes, forming gold-molecule-gold structures. The investigation into these molecular junctions' electrical and thermoelectric behaviour relies on theoretical approaches detailed in Chapters 2 and 3. Chapter 2 introduces the principles of density functional theory DFT, while Chapter 3 provides an overview of transport theory, emphasizing Green's function formalism. Chapter 4 examines the electron transport properties of cross-linked molecular junctions, consisting of a dimer formed by two OPE3 molecules connected through two different bridges. These junctions feature six connection points with thiol groups (SH). To validate the findings, three theoretical approaches are employed: the orbital product rule OPR, the tight-binding model TBM, and density functional theory DFT calculations. Additionally, these cross-linked systems' electrical conductance and Seebeck coefficient are analysed using DFT simulations. Chapter 5 explores the impact of the bridge type on electron transport properties by studying another two different bridge configurations in the junctions. Finally, this thesis is concluded with a summary and future works in chapter 6.