Archive of Much Older Research Projects

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Dear visitor, do you really want to se this ancient (as in, last major update in 2007 or so) page? Not the current research page??? Well, if you are sure, then please enjoy! Old Pictures The following pages contain a few old pictures relating to various topics that are discussed elsewhere on this page. A web article on our research in the area of of theoretical actinide molecular sciences (March 2001). The following two figures are also included in this article: Figure showing the proposed non-aqueous potential energy surface for the intramolecular exchange of uranyl and hydroxide oxygen atoms in uranyl tetrahydroxide (VI), UO2(OH)42- (1998). Figure showing the (experimentally unknown) "cis"-uranyl structures (1999). Calculated and experimental 125Te chemical shifts in various compounds of tellurium (1997). Density functional calculations of molecular ESR g-tensors (1997). Some Older Projects This section contains an incomplete list of older research projects in approximately revers chronologocial order. Most of these are completed, although a few are still ongoing in some form. Theoretical Actinide Molecular Science: Actinide Elements in Aqueous Solution (1997-ongoing) We are using DFT to explore the chemistry and spectroscopic properties of complexes that are likely to form if the radioactive element enters the ground water at contaminated sites. So far, we have studied molecules such as the aquo complexes of AnV and AnVI where An = U, Np, Pu, or the carbonate, nitrate, chloride and hydroxide complexes of uranium (VI). The aquo complexes, in particular, serve as a testing ground for the various approximations that are required in practical calculations on actinide compounds.       For these studies, all of relativity (including spin-orbit), electron-electron correlation, multiplet effects and solvent effects have to be accounted for. This results in a formidable challenge for theory to accurately predict the properties of these complexes. Theoretical Actinide Molecular Science: Complexes with Macrocycles (2005-ongoing) Closely related to the preceeding project, we are studying complexes that have been used, or might become useful, for the selective extraction of actinide elements from mixed (waste) solutions. Typical extraction agents are large, multidentate organic molecules that can, in principle, be tailored to selectively bind a specific heavy metal in a specific oxidation state.       Macrocycles that can incorporate the metal into their cavity are prominent examples in this category. Currently, we are studying complexes of uranium, neptunium and plutonium in the V and VI oxidation states with crown ether and expanded porphyrin ligands (such as alaskaphyrin, amethyrin, isomaethyrin, pentaphyrin, texaphyrin, sapphyrin, oxosapphyrin) among other systems.       We try to answer questions regarding, for instance, the importance of and reasons for ligand planarity or the stabilization of the pentavalent oxidation state of the metal. We are also interested in structures, bonding, vibrational frequencies, reaction mechanisms, relative stability, etc. Theoretical Actinide Molecular Science: Evaluation of Methods (2005-ongoing) At least four different levels of approximation are required in applying quantum chemistry to molecules of the actinides, viz. (i) an approximate relativistic method, (ii) approximations for the treatement of the electron-electron correlation, (iii) solvent models for the bulk solvent environment, and (iv) for large ligands that might not be amenable to accurate computational studies, the choice of truncated model systems. The critical evaluation of these various approximations is an ongoing effort. Theoretical Studies of Lithium Amides: Effects of Solvation, Aggregation and Complexation (2001-2/2006-7) We have initiated a theoretical study of monomeric, dimeric, and trimeric lithium amide complexes. Experimentally, perhaps the most important species are the dimers with a central, four-membered Li2N2 ring as their common feature.       We aim at a better understanding of the electronic structure, complex equilibria, role of the solvent molecules, degrees of coordination, ligand bonding modes and similar properties of these molecules. Moreover, we want to correlate the 7Li NMR signature and other spectroscopic properties (such as heteronulcear NMR and vibrational frequencies) to the specific structural details of the complexes. This requires to analyze and understand in detail how the structural properties on one hand and the spectroscopic observables on the other hand are related to the details of the electronic structure. Development of a Band-Structure Approach for the Calculation of NMR and ESR Parameters (2002-6) In this project, we are developing a solid state (band-structure) approach for the calculation of NMR and ESR parameters. The actual code development is being done within the environment of the ADF electronic-structure programs. Initially, we are extending the molecular GIAO approach for the NMR chemical shift to the solid state. (GIAO stands for 'gauge-including atomic orbitals'.) Subsequently, we want to cover other properties such as the ESR g-tensor, NMR spin-spin coupling constants, or the ESR fine structure constants. Analysis of NMR and ESR Parameters (2007-8) We are interested in developing new computational tools for analyzing calculated NMR/ESR parameters in terms of the electronic structure. Computational Study of Hydroxyproline Derivatives (2006-10) In collaboration with the group of Dr. F. Schweizer (Department of Chemistry, University of Manitoba), we are investigating the structures and spectroscopic properties of fused and spirocyclic hydroxyproline analogues. Of particular interest is the Cis-Trans isomerization. Dye-Sensitized Solar Cells (DSSCs) (2006-ongoing) We apply the unique tools of quantum chemistry to gain a better understanding of elementary, molecular processes in DSSCs. A detailed understanding will be the foundation for dramatic improvements in efficiency that are required to make this evolving technology applicable on a large scale. Theoretical Actinide Molecular Science: Uranium Fluorides and Oxofluorides (2004-2007) By choosing experimental gas-phase data for small molecules - fluorides and oxofluorides of uranium (VI), (V) and (IV) - as reference points, we have tested the different levels of approximation involved in quantum-chemical calculations. Theoretical Actinide Molecular Science: Actinyl Complexes of Alaskaphyrin and Related Macrocycles (2004-6) In this project (which is part of our larger program aimed at understanding the chemistry of inclusion complexes between actinide species and various macrocycles), we have investigated the actinyl inclusion complexes formed with the N-donor, pyrrol-based, "expanded-porphyrin" macrocycle alaskaphyrin as well as with some related macrocycles. Theoretical Actinide Molecular Science: Accurate Study of Actinyl Aquo Complexes (1998-2000/2004-5) As part of our ongoing investigations into the nature and bonding of actinide species in aqueous solution, we have completed detailed studies of the actinyl aquo complexes [AnO 2(H2O)m]n+, An = U, Np, Pu and N = 1, 2. Some of our findings include (i) critical investigation and, as a consequence, better understanding of model chemistries and solvation models as applied to actinide complexes; (ii) accurate prediction of the free energies of hydration for the entire series of complexes; (iii) accurate calculation of the An(VI)/An(V) reduction potential. Theoretical Actinide Molecular Science: NMR Properties of Uranium (VI) Complexes (1998-2004) We have tried to calculate both, ligand and 235U chemical shifts in diamagnetic compounds of uranium. We have shown that various relativistic DFT methods (with the exception of the large-core ECP approach) are useful for predicting NMR chemical shifts in these systems. Thus, DFT-NMR calculations are capable of covering the entire periodic table.       We have studied the effects of solvation, of the particular relativistic approximation, and of the exchange-correlation (XC) functional on the calculated chemical shifts. Moreover, we have explored the scope of the potential chemical shift range for the 235U nucleus. We predict a chemical shift range of over 35,000ppm. (Experimental actinide metal chemical shifts are as yet unknown.) Separately, we are investigating the magnitude of spin-orbit effects on proton (1H) NMR chemical shifts. DFT Calculations of ESR G-Tensors (See here for some older work in this area.) Electronic-Structure Calculations for NMR Quantum Computing (2002-2003) We have applied DFT methods to calculate the NMR chemical shifts and spin-spin coupling constants in molecules that had been used - or might become useful - for the construction of NMR-based experimental quantum computers. This project involved a critical evaluation of the quantum-chemical methods and an assessment of the design criteria for molecules used in quantum computing (such as, for instance, the requirement of chemical shift dispersion.) We have proposed new target molecules to be used in quantum computing. Theoretical Foundation of the GIAO Method (1995-6/2001-2) We have explicitly derived the theoretical correspondence between the GIAO ("gauge-including atomic orbitals") approach for the NMR shielding tensor and the simpler "common-gauge" method. An important side result is a better understanding of the different terms that appear in the GIAO formulation. Theoretical Study of the Catalytic NOx Abatement in Cu-Exchanged ZSM-5 (2000-2001) While working in the CLRC Daresbury Laboratory (Warrington, UK), I collaborated in a project that aimed at developing and applying QM/MM (quantum mechanics/molecular mechanics) methods. In particular, these new methods where applied to modeling catalytic processes inside a copper-exchanged zeolite. Theoretical Actinide Molecular Science: UF6 Derivatives (1997-2002) We have studied derivatives of UF6, UF6-nLn, L = Cl and OCH3 and n = 0 - 6. In particular, we have predicted the structures, vibrational frequencies and intensities, and NMR chemical shifts. We have used the calculated vibrational parameters to help assign experimental spectra. Moreover, we have looked at periodic trends in the electronic structure of these compounds. Theoretical Actinide Molecular Science: Theoretical Study of [UO2X4]2- species, X = F, Cl, OH (1997-1999) In an initial study for the larger actinide project, we have studied the title species in some detail. Thus, we have investigated the possible conformers of uranyl (VI) tetrahydroxide, [UO2(OH)4]2- where we found experimentally unknown "cis" species with a bend uranyl unit. We have also proposed possible reaction pathways for the intramolecular oxygen exchange. "Cis" conformers were also found for the fluoride and chloride species. DFT Calculations of Metal NMR Chemical Shifts (1994-1997) In this project, we have used DFT to calculate metal NMR chemical shifts. The calculations served as a validation of our newly developed DFT methods, and we have also used them to interpret or explain trends in the observed chemical shifts. See here for an example.