Steven R. Kirk

Pointing the way to the products? Comparison of the stress tensor and the second-derivative tensor of the electron density

The eigenvectors of the electronic stress tensor can be used to identify where new bond paths form in a chemical reaction. In cases where the eigenvectors of the stress tensor are not available, the gradient-expansion-approximation suggests using the eigenvalues of the second derivative tensor of the electron density instead; this approximation can be made quantitatively accurate by scaling and shifting the second-derivative tensor, but it has a weaker physical basis and less predictive power for chemical reactivity than the stress tensor. These tools provide an extension of the quantum theory of atoms and molecules from the characterization of molecular electronic structure to the prediction of chemical reactivity.

Information theory-based software metrics and obfuscation

Abstract A new approach to software metrics using concepts from information theory, data compression, complexity theory and analogies with real physical systems is described. A novel application of software obfuscation allows an existing software package to be analysed in terms of the effects of perturbations caused by the obfuscator. Parallels are drawn between the results of the software analysis and the behaviour of physical systems as described by classical thermodynamics.

Structures, energies and bonding in neutral and charged Li microclusters

Structural and chemical properties of charged and neutral Lithium microclusters are investigated for

Biochar sulfonic acid immobilized chlorozincate ionic liquid: an efficiently biomimetic and reusable catalyst for hydrolysis of cellulose and bamboo under microwave irradiation

{\text{Li}}_n^q(n = {5} - {1}0,q = 0,\pm {1})

The Ehrenfest force topology: a physically intuitive approach for analyzing chemical interactions

. A total of 18 quantum conformational spaces are randomly walked to produce candidate structures for local minima. Very rich potential energy surfaces are produced, with the largest structural complexity predicted for anionic clusters. Analysis of the electron charge distributions using the quantum theory of atoms in molecules (QTAIM) predicts major stabilizing roles of Non–nuclear attractors (NNAs) via NNA···Li interactions with virtually no direct Li···Li interactions, except in the least stable configurations. A transition in behavior for clusters containing more than seven nuclei is observed by using the recently introduced quantum topology to determine in a quantum mechanically consistent fashion the number of spatial dimensions each cluster has. We experiment with a novel scheme for extracting persistent structural motifs with increase in cluster size. The new structural motifs correlate well with the energetic stability, particularly in highlighting the least stable structures. Quantifying the degree of covalent character in Lithium bonding independently agrees with the observation in the transition in cluster behavior for lithium clusters containing more than seven nuclei. Good correlation with available experimental data is obtained for all properties reported in this work.

Exploring hydrogen bond in the excited state leading toward intramolecular proton transfer: detailed analysis of the structure and charge density topology along the reaction path using QTAIM

Structural and chemical properties of the building block of silica nanowires, (SiO(2))(6), are investigated with the theory of atoms and molecules (QTAIM). Twenty-five conformers have been analyzed, ten of which have not been reported before. We extend the silica (SiO(2))(6) topology phase space using QTAIM; the Poincaré-Hopf topological sum rules are applied and used to identify the spanning set of topologies, and this includes finding eight new distinct topologies that satisfy the Poincaré-Hopf relation. A simple phase diagram of the solutions of the Poincaré-Hopf relation is created with the aid of a new classification scheme to determine the boundary between topological stability and instability. Sum rules are then found to be applicable to any set of isomers. We determine that O-O bonding interactions exist for the silica (SiO(2))(6) conformers in regions where the energy surface is flattest. In addition, we identify unstable local minima in the topology of the charge density in order to further compare conformer instabilities. We quantify the dimensionality of a molecule using the Poincaré-Hopf relation instead of Euclidean geometry. This quantum topological definition of geometry shows that the four most energetically stable (SiO(2))(6) conformers are quantified as two-dimensional within the new quantum topology.

Tiling for Performance Tuning on Different Models of GPUs

A chlorozincate ionic liquid-functionalized biochar sulfonic acid (BC-SO3H-IL-Zn) was designed and conveniently prepared via multistep processes, involving the syntheses of biochar sulfonic acid (BC-SO3H) and 1-trimethoxysilylpropyl-3-methylimidazolium chloride (IL)-ZnCl2 (IL-Zn), followed by grafting the IL-Zn onto BC-SO3H. The proposed catalyst was found to show a much higher turnover number (TON, 5.91 for cellulose and 1.78 for bamboo) for the microwave-assisted hydrolysis of cellulose and bamboo to reducing sugars (RSs) in water compared to the corresponding IL-functionalized BC-SO3H (BC-SO3H-IL, TON, 3.23 for cellulose and 0.46 for bamboo) and BC-SO3H (TON, 1.51 for cellulose and 0.15 for bamboo). Furthermore, it, like BC-SO3H-IL, possessed an excellent repeatability for cellulose hydrolysis. The excellent catalytic performance of BC-SO3H-IL-Zn is likely due to the following reasons: Firstly, the introduction of ZnCl2 bestows the catalyst with a delignification function. Secondly, in comparison with the OH groups of BC-SO3H, the IL and especially IL-Zn groups flexibly bound to BC-SO3H, like cellulose binding domain of cellulose, show an stronger affinity for cellulose molecules, on the other hand, they play a better synergistic role and improved acidity in the SO3H groups (as a catalysis domain of cellulase) catalyzing cleavage of the β-1,4-glycosidic bonds of cellulose, as supported by the adsorption experiments of catalysts to oligosaccharides, their thermogravimetric analysis and catalytic reaction results.Graphical AbstractChlorozincate ionic liquid functionalized biochar sulfonic acid (BC-SO3H-IL-Zn) proposed by us was found to be an efficiently biomimetic catalyst for the heterogeneous hydrolysis of cellulose and lignocelluloses to RSs and 5-hydroxymethyl furfural (5-HMF) under microwave irradiation.

A bond, ring and cage resolved Poincaré–Hopf relationship for isomerisation reaction pathways

A novel hollow-structured Mn/TS-1 catalyst has been reported as a non-nitric acid route for adipic acid production from oxidative cleavage of cyclohexanone. The method generates adipic acid in high yields with molecular oxygen under organic solvent- and promoter-free conditions. The hollow nature of the catalyst with large intra-particle voids facilitates the diffusion of bulky molecules to the internal catalytic site and increases the catalyst activity. The advantage of this catalyst is its reusability with almost consistent reactivity, thereby making it viable for industrial applications.