Gas Phase Computational Studies on the Competition between Nitrile and Water Ligands in Uranyl Complexes

The gas phase formation of uranyl dicationic complexes containing water and nitrile (acetonitrile, propionitrile, and benzonitrile) ligands, [UO2(H2O)m(RCN)n]2+, has been studied using density functional theory with a relativistic effective core potential to account for scalar relativistic effects on uranium. It is shown that nitrile addition is favored over the addition of water ligands. Decomposition of these complexes to [UO2OH(H2O)m(RCN)n]+ by the loss of either H3O+ or (RCN + H)+ is also examined. It is found that this reaction is competitive with the ligand addition when the coordination sphere of uranyl is unsaturated. Additionally, this reaction is influenced by the size of the nitrile ligand with reactions involving acetonitrile being the most prevalent. Finally, ligand addition to the monocation shows trends similar to that of the dication with energetic differences being smaller for the addition to the monocation

Development of High Performance Scientific Components for Interoperability of Computing Packages

Three major high performance quantum chemistry computational packages, NWChem, GAMESS and MPQC have been developed by different research efforts following different design patterns. The goal is to achieve interoperability among these packages by overcoming the challenges caused by the different communication patterns and software design of each of these packages. Developing a chemistry algorithm is a time consuming process; integration of large quantum chemistry packages will allow resource sharing and thus avoid reinvention of the wheel. Creating connections between these incompatible packages is the major motivation of our work. We achieve this interoperability by bringing the benefits of Component Based Software Engineering through a plug-and-play component framework called Common Component Architecture (CCA). In this paper, we present a strategy and process used for interfacing two widely used and important computational chemistry methodologies: Quantum Mechanics and Molecular Mechanics. This paper also demonstrates the performance evaluation of these CCA compliant components to show the feasibility of the proposed approach and finally discusses the current research issues

On the Formation of “Hypercoordinated” Uranyl Complexes

Recent gas-phase experimental studies suggest the presence of hypercoordinated uranyl complexes. Coordination of acetone (Ace) to uranyl to form hypercoordinated species is examined using density functional theory (DFT) with a range of functionals and second-order perturbation theory (MP2). Complexes with up to eight acetones were studied. It is shown that no more than six acetones can bind directly to uranium and that the observed uranyl complexes are not hypercoordinated. In addition, other more exotic species involving proton transfer between acetones and species involving enol tautomers of acetone are high-energy species that are unlikely to form

Roles of Acetone and Diacetone Alcohol in Coordination and Dissociation Reactions of Uranyl Complexes

Combined collision-induced dissociation mass spectrometry experiments with DFT and MP2 calculations were employed to elucidate the molecular structures and energetics of dissociation reactions of uranyl species containing acetone and diacetone alcohol ligands. It is shown that solutions containing diacetone alcohol ligands can produce species with more than five oxygen atoms available for coordination. Calculations confirm that complexes with up to four diacetone alcohol ligands can be energetically stable but that the effective number of atoms coordinating with uranium in the equatorial plane does not exceed five. Water elimination reactions of diacetone alcohol ligands are shown to have two coordination-dependent reaction channels, through formation of mesityl oxide ligands or formation of alkoxide and protonated mesityl oxide species. The present results provide an explanation for the implausible observation of “[UO2(ACO)6,7,8]2+” in and observed water-elimination reactions from purportedly uranyl–acetone complexes (Rios, D.; Rutkowski, P. X.; Van Stipdonk, M. J.; Gibson, J. K. Inorg. Chem.2011, 50, 4781)

Uncontracted Rys Quadrature Implementation of up to G Functions on Graphical Processing Units

An implementation is presented of an uncontracted Rys quadrature algorithm for electron repulsion integrals, including up to g functions on graphical processing units (GPUs). The general GPU programming model, the challenges associated with implementing the Rys quadrature on these highly parallel emerging architectures, and a new approach to implementing the quadrature are outlined. The performance of the implementation is evaluated for single and double precision on two different types of GPU devices. The performance obtained is on par with the matrix−vector routine from the CUDA basic linear algebra subroutines (CUBLAS) library

A Protocol for the Evaluation of Coverall Fit

Evaluating fit is an inexact science and can be very subjective based on the wearers’ or judges’ preference and perceptions (Yu, 2004). The use of expert judges is the most common method of evaluating fit (Yu, 2004; Watkins, 1995). This paper proposes a protocol to triangulate the assessment of expert judges in evaluating the fit of protective coveralls. Protection from the environment is the main function of protective coveralls The functionality and fit of current protective coveralls is generally poor, and researchers have shown that wearability and fit of coveralls affect compliance with established safety standards (Ashdown & Watkins, 1992; Huck, Maganga, & Kim, 1997)