In Search of a Computational Approach to Gold Chemistry Within Density Functional Theory
Author | : |
Publisher | : |
Total Pages | : 338 |
Release | : 2014 |
ISBN-10 | : OCLC:903950961 |
ISBN-13 | : |
Rating | : 4/5 (61 Downloads) |
Book excerpt: This computational study investigates two aspects of gold chemistry within the density functional theory (DFT) framework. The first involves an accurate prediction of the optical properties of small gold nanoclusters and the second concerns a correct description of gold-ligand, donor-acceptor interactions. The optical properties of gold clusters attract a great deal of interest in the scientific community due to their potential use in nanotechnology, analytical techniques and medicine. These clusters are the basic elements in the assembly of nanostructures where ligands serve as a stabilizing agents, control the functionality and prevent further aggregation. A proper account of gold-ligand interactions is essential for the further understanding of self-assembly processes and coordination chemistry. The absorption UV spectra of "magic" gold clusters have been investigated with time-dependent density functional theory (TDDFT).The calculations employ long-range corrected (LRC) functionals, subjected to first-principles tuning by varying the range-separation parameter. This approach is known to ameliorate a well-known failure of TDDFT-the appearance of spurious, low-energy charge transfer excitations. The results are compared to experimental spectra and benchmark computations. For all well performing LRC functionals the magnitude of HOMO-LUMO gaps compares well to the experimental fundamental gaps. Donor-acceptor interactions are notoriously difficult and unpredictable for conventional DFT methodologies. These interactions require a proper account of the ionization potential of the electron donor and electron affinity of the electron acceptor. We propose a reliable computational treatment of gold-ligand interactions within the GKS framework. It utilizes a two-parameter tuning scheme for monomer properties ensuring that a common functional, optimal for both the donor and acceptor, is found. The binding energies are computed for the interaction of Au4 with several model ligands. The results agree with coupled-cluster reference values- for the right reasons. This dissertation further shows that a system-dependent long-range correction and the inclusion of a fixed portion of exact exchange are essential for accurate prediction of optical properties and gold-ligand donor-acceptor interactions. A proper account of relativistic effects is necessary for the correct description the chemistry and spectroscopy of gold and the dispersion contribution is required for a reliable DFT approach for gold-ligand interactions.