Embedding Theory: Applications and Development

Abstract

This dissertation focuses on the application of density functional embedding theory (DFET), as well as the numerical implementation, verification, and analysis of potential functional embedding theory (PFET). Density functional theory (DFT) is widely used to study the properties of bulk solids and surfaces, but it fails to describe certain phenomena. Correlated wavefunction (CW) methods describe electronic structure more accurately. However, their application is typically limited to molecules of small size. The embedded CW (ECW) scheme combines the two families of methods together within a rigorous theoretical framework. ECW methods generally treat the local region of interest at the CW level and describe the extended environment at the DFT level, thus striking a balance between efficiency and accuracy. We apply the DFET-based ECW method to explore the role of orientational degrees of freedom in the dissociative adsorption of O2 onto an Al (111) surface and proposed a mechanism that reconciles seemingly contradictory experimental findings. In another application, we study the ground state and excited states of H2 adsorbed on the Au (111) surface with the DFET-based ECW method. The ECW results provide evidence that the hot electrons induced by surface plasmons do indeed enable the dissociation of H2 at room temperature. To go beyond the DFET scheme, we implement the PFET scheme at the CW/DFT level for a more rigorous description of the interaction between the subsystems. We first numerically implement the PFET scheme using a Gaussian-type-orbital/planewave (pw) hybrid basis set to achieve general usability and verify its performance at a pure DFT/DFT level. We further examine and analyze the performance of the PFET scheme at a hybrid CW/DFT level in comparison with the DFET-based ECW method and an intermediate, DFET/PFET-based method. The test calculations on a variety of the systems representing three bonding types (hydrogen, metallic, and ionic bonds) demonstrate the superior robustness and accuracy of the PFET scheme compared with the other two. We find that the appropriate interaction between the subsystems at the CW/DFT level provided by the PFET scheme is particularly essential to study the properties of adsorbates on ionic surfaces.