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Density functional theory BLYP (Becke's exchange and Lee-Yang-Parr's correlation functionals), ab initio Hartree-Fock (HF) and hybrid DFT/HF B3LYP calculations were carried out to study the structure and vibrational spectra of quadricyclane. The BLYP/6-31G* and scaled HF/6-31G* frequencies correspond well with each other and with available experimental assignment of the fundamental vibrational modes. Based on conformity between the calculated and experimental results, a plausible assignment of two remaining a1 modes and all non-CH stretching a2, b1, and b2 modes is proposed.

The London dispersion interaction is responsible for attraction between non-polar molecules and is of great importance in describing structure and reactivity in many areas of chemistry. Dispersion is difficult to model accurately. Density Functional Theory (DFT) methods, widely used in computational chemistry today, do not include the necessary physics. This often leads to qualitatively incorrect predictions when DFT is applied to dispersion-bound systems. A novel DFT method has been developed which is capable of accurately modeling dispersion. Dispersion attraction between molecules arises when an instantaneous dipole moment in one molecule induces a dipole moment in a second molecule. Our approach proposes that the source of these instantaneous dipole moments is the position-dependent dipole moment of the exchange hole. The model is no more computationally expensive than existing DFTs and gives remarkably accurate dispersion coefficients, intermolecular separations, intermolecular binding energies, and intramolecular conformational energies. Our dispersion theory is also combined with previous post-exact-exchange models of dynamical and nondynamical correlation, yielding a unified exact-exchange-based energy functional called DF07. DF07 overcomes many of the outstanding problems in DFT arising from local exchange approximations. The DF07 model is shown to provide highly accurate results for thermochemistry, kinetics, and van der Waals interactions. / Thesis (Ph.D, Chemistry) -- Queen's University, 2007-11-29 21:57:09.045

Graphene oxide (GO) is a material of both fundamental and applied interest. Elucidating this complex material is crucial to both control its physical chemical properties and enable its applications in technology. Graphene oxide films synthesized from epitaxial graphene on silicon carbide constitute a particular -- simplified -- form of GO, suitable for fundamental physical chemistry studies of oxidized sp2 carbon materials. In this thesis work, I used density functional theory calculations and I developed a lattice-model Monte Carlo scheme to elucidate puzzling experimental observations and to gain molecular insight into the chemical composition, thermochemical and structural properties of this type of ultrathin GO films on silicon carbide substrates.

archives@tulane.edu / Abstract: A search in a research database for “large specific rotation” or anything similar produces few articles. Large specific rotation is not commonly used as an indicator for extraordinary chiroptical response. Alternatively, anisotropy factors obtained from circular dichroism spectra and calculated rotational strengths are more widely used to gauge chiroptical response. To another point, a search for “large chiroptical response” gives few articles that discuss pure organic compounds, and the result list is populated by organometallic clusters, nanostructures, and thin films. A search of the Reaxys database for organic compounds with [α]Ds larger than 1000 revealed that there are about 600, and there are only two that have [α]Ds larger than 10,000.30 We wondered if we could design a compound that would break the record in specific rotation and possess extraordinary chiroptical properties. Guided by time-dependent density functional theory (TD-DFT) calculations, various chiral, polycyclic aromatic compounds (PACs) were chosen as candidates to display extraordinary chiroptical properties, such as high optical rotation, strong circular dichroism, or a high degree of circularly polarized luminescence (CPL). PACs comprise a large class of organic compounds. In addition to synthetic PACs, numerous naturally occurring PACs exist in coal tar and as decomposition products of organic material. Since their pi electrons are delocalized, PACs have interesting and possibly useful electronic properties and a variety of applications. The PACs described in this dissertation, e.g., helical mesobenzanthrones, a cyclophane, are twisted pentacenes are chiral and have interesting optoelectronic properties. TD-DFT was primarily used to predict which compounds had the greatest potential to yield record-breaking specific rotations or other chiroptical properties, and ordinary DFT calculation were used to determine if these compounds had sufficiently high racemization barriers to be resolved at room temperature. With regard to specific rotation, the accuracy of TD-DFT calculations was examined by comparing experimental specific rotations to the calculated values. / 1 / Kelly Jane Dougherty

Over the years electronic structure theory has proven to be a powerful method with which one can probe the behaviour of materials, making it possible to describe and predict material properties. The numerical tools needed for these methods are always in need of development, since the desire to calculate more complex materials pushes this field forward. This thesis contains work on both this implementational and developmental aspects. It begins by reviewing density functional theory and dynamical mean field theory, with the aim of merging these two methods. We point out theoretical and technical issues that may occur while doing this. One issue is the Padé approximant, which is used for analytical continuation. We assess the approximant and point out difficulties that can occur, and propose and evaluate methods for their solution. The virial theorem is assessed within the framework of density functional theory merged with many-body methods. We find that the virial theorem is extended from its usual form, and confirm this by performing practical calculations. The unified theory of crystal structure for transition metals has been established a long time ago using early electronic structure calculations. Here we implement the first- principles exact muffin-tin orbitals method to investigate the structural properties of the 6d transition metals. The goal of our study is to verify the existing theory for the mostly unknown 6d series and the performance of the current state-of-the art in the case of heavy d metals. It is found that these elements behave similarly to their lighter counterparts, except for a few deviations. In these cases we argue that it is relativistic effects that cause this anomalous behaviour. Palladium is then studied, taking many-body effects into account. We find that we can reproduce experimental photoemission spectra by these methods, as well as the Fermi surface. The thesis ends with an investigation of the stacking fault energies of the strongly correlated metal cerium. In addition to providing the first ab-initio stacking fault data for the two cubic phases of Ce, we discuss how these results could have an impact on the interpretation of the phase diagram of cerium / <p>QC 20150522</p>