Search

The theory of adiabatic electron transport in a correlated condensed-matter system is rooted in a seminal paper by Niu and Thouless [J. Phys. A: Math. Gen. 17, 2453 (1984)]; I adopt here an analogous logic in order to retrieve the known expression for the adiabatic electronic flux in a molecular system [L. A. Nafie, J. Chem. Phys. 79, 4950 (1983)]. Its derivation here is considerably simpler than those available in the current quantum-chemistry literature; it also explicitly identifies the adiabaticity parameter, in terms of which the adiabatic flux and the electron density are both exact to first order. It is shown that the continuity equation is conserved to the same order. For the sake of completeness, I also briefly outline the relevance of the macroscopic electronic flux to the physics of solids and liquids. [ABSTRACT FROM AUTHOR]

The [3+2] cycloaddition (32CA) reaction between difluoromethyl diazomethane (DFDAM) and 3-ylideneoxindole (3YOI) has been studied using molecular electron density theory at the M06-2X/6-311+G(d,p) computational level. ELF topological analysis of DFDAM characterizes this three-atom-component (TAC) as a pseudoradical species participating in the pseudomonoradical (pmr)-type 32CA reactions. Analysis of the conceptual DFT reactivity indices indicates that along a polar reaction 3YOI will act as the electrophile while DFDAM will act as the nucleophile. This 32CA reaction presents low activation enthalpy in dichloromethane, 8.2 kcal mol−1. The reaction is endo selective and completely ortho regioselective in agreement with the experimental outcome. The strong exergonic character of this 32CA reaction, −18.9 kcal mol−1, makes it irreversible. The high global electron density transfer found at the most favorable ortho/endo TS, 0.24e, accounts for the highly polar character of this 32CA reaction, classified as the forward electron density flux. BET analysis along the most favourable ortho/endo reaction path asserts the pmr-type reactivity of this TAC. This 32CA reaction takes place through a non-concerted two-stage one-step mechanism characterized by the initial C–C single bond formation involving the pseudoradical C3 carbon of DFDAM. [ABSTRACT FROM AUTHOR]

A system of one-dimensional multigroup equations for the first three moments of the electron distribution function in the range of intermediate and high energies is derived. The system includes equations for the balance of concentration, flux density and momentum flux density of electrons and it is intended for numerical simulations of processes involving fast electrons in weakly ionized cold plasma. [ABSTRACT FROM AUTHOR]

The site-, regio-, and stereo-selectivities of the title reactions have been studied using density functional theory (DFT) at the M06/6-311G(d,p) level of theory. The effects of substituents on both the three-atom component (TAC) and norbornadiene derivatives have been investigated with a focus on the site-selectivity. The reaction of benzylazide with (1S,4R)-2-tosyl-7-oxabicyclo[2.2.1]hepta-2,5-diene and (1R,4S)-2-bromo-3-tosyl-7-oxabicyclo[2.2.1]hepta-2,5-diene proceeds via addition across the substituted olefinic bond of the two norbornadiene derivatives. Substituents on the TAC do not affect the selectivity of the reaction while substituents on the norbornadiene significantly affect the selectivity of the reaction. Benzylazide preferentially adds across the substituted olefinic bond of the norbornadiene derivative when strong electron-withdrawing group (EWGs) and electron-releasing group (ERGs) substituents are on the norbornadiene while weak ERGs and EWGs on the norbornadiene significantly decreases the site-selectivity such that addition across either double is no longer favored over the other. The formation of exo-cycloadducts is generally favored over the endo-cycloadducts. The reaction of benzylazide and norbornadiene derivatives is a highly irreversible exergonic reaction. The direction of electron density flux is dependent on the nature of the substituent on the reactants. Global reactivity indices and Parr function calculations are in good agreement with the activation barriers and the selectivity of the reactions. [ABSTRACT FROM AUTHOR]

The high heat fluxes to the divertor during edge localised mode (ELM) instabilities have to be reduced for a sustainable future tokamak reactor. A solution to reduce the heat fluxes could be the Super-X divertor, which will be tested on MAST-U. ELM simulations for MAST-U Super-X tokamak plasmas have been obtained, using JOREK. A factor 10 decrease in the peak heat flux to the outer target and almost a factor 8 decrease in the ELM energy fluence when comparing the Super-X to a conventional divertor configuration has been found. A detached MAST-U case, after the roll-over in the target parallel electron density flux, is used as a starting point for ELM burn-through simulations. The plasma burns through the neutrals front during the ELM causing the divertor plasma to re-attach. After the crash a transition back to detachment is indicated, where the recovery to pre-ELM divertor conditions occurs in a few milliseconds, when the neutral pressure is high in the divertor. Recovery times are shorter than the inter-ELM phase in previous MAST experiments. The peak ELM energy fluence obtained after the ELM burn-through is 0.82 kJ/m2, which is significantly lower than that predicted from the empirical scaling of the ELM energy fluence - indicating promising results for future MAST-U operations. [ABSTRACT FROM AUTHOR]

In the present work, various scenarios of the spatial distributions of argon dusty plasma parameters are considered, focusing on the case of a large density of dust particles. It is shown that in this case a scenario with the inversion of the ambipolar field sign, considered in earlier studies by authors for plasma with heavy negative ions, can be realized. In this case, the ionization inside the dust cloud becomes small in comparison with the volume loss of charges inside the dust cloud, and the lack of charges is compensated by their arrival from the outer peripheral plasma region. This transition is accompanied by the phenomenon of the reversal of the sign of the radial electric field at the boundary of the dust cloud, and the formation of nonmonotonic profiles of the electron density with a shift of the maximum electron density from the center to the periphery. The radial stability of the dust particles cloud is provided by the balance of the increasing dust charge density gradient in the presence of the pushing out ambipolar field. [ABSTRACT FROM AUTHOR]

The aim of the present contribution is to provide a framework for analyzing and visualizing the correlated many-electron dynamics of molecular systems, where an explicitly time-dependent electronic wave packet is represented as a linear combination of N-electron wave functions. The central quantity of interest is the electronic flux density, which contains all information about the transient electronic density, the associated phase, and their temporal evolution. It is computed from the associated one-electron operator by reducing the multideterminantal, many-electron wave packet using the Slater-Condon rules. Here, we introduce a general tool for post-processing multideterminant configuration-interaction wave functions obtained at various levels of theory. It is tailored to extract directly the data from the output of standard quantum chemistry packages using atom-centered Gaussian-type basis functions. The procedure is implemented in the open-source Python program detCI@ORBKIT, which shares and builds on the modular design of our recently published post-processing toolbox (Hermann et al., J. Comput. Chem. 2016, 37, 1511). The new procedure is applied to ultrafast charge migration processes in different molecular systems, demonstrating its broad applicability. Convergence of the N-electron dynamics with respect to the electronic structure theory level and basis set size is investigated. This provides an assessment of the robustness of qualitative and quantitative statements that can be made concerning dynamical features observed in charge migration simulations. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The regioselective zw-type [3 + 2] cycloaddition (32CA) reactions of a series of aryl-substituted nitrile N-oxides (NOs) with trichloronitropropene (TNP) have been both experimentally and theoretically studied within the Molecular Electron Density Theory (MEDT). Zwitterionic NOs behave as moderate nucleophiles while TNP acts as a very strong electrophile in these polar 32CA reactions of forward electron density flux, which present moderate activation Gibbs free energies of 22.8–25.6 kcal·mol−1 and an exergonic character of 28.4 kcal·mol−1 that makes them irreversible and kinetically controlled. The most favorable reaction is that involving the most nucleophilic MeO-substituted NO. Despite Parr functions correctly predicting the experimental regioselectivity with the most favorable O-CCCl3 interaction, these reactions follow a two-stage one-step mechanism in which formation of the O-C(CCl3) bond takes place once the C-C(NO2) bond is already formed. The present MEDT concludes that the reactivity differences in the series of NOs come from their different nucleophilic activation and polar character of the reactions, rather than any mechanistic feature. [ABSTRACT FROM AUTHOR]

The reactivity of the 5-arylidenerhodanine and 5-arylideneisorhodanine derivatives in reactions with dimethyl maleate was computationally studied at the DFT(M06-2X)/6–311+G(d,p) theory level. Eight stereoisomers of the reaction products were considered. The effect of the solvent was taken into account by means of the continuous and discrete models for acetic acid (PCM and three CH3COOH molecules). Aromatic stabilization of the transition states was documented by the values of HOMA, NICS(0), and NICS(1) indices. The higher reactivity of the isorhodanine derivative was associated with a relatively low activation energy, ∆Ea (15.2–22.3 kcal mol–1), which is needed to cross the TS. For the rhodanine derivative, higher values of ∆Ea (34.1–36.1 kcal mol–1) were obtained. The reactivity was also studied from the perspective of the frontier molecular orbitals, the energy gaps between the HOMO and LUMO, the flux of electron density, the Fukui functions, f+(r), f−(r), and f0(r), and the global indexes defined in the conceptual DFT, i.e., the electronic chemical potential, chemical hardness, global electrophilicity, and empirical nucleophilicity index. [ABSTRACT FROM AUTHOR]