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[en] Radiation-chemical yields of electron-ion pair BeOi''+ - e''- formed from direct one fold ionization of the products -different electron-excitation states (1''1Π(V), 2''1Σ''+(V), 1''1Δ(V), 2''1Π(V), 3''1Π(R), 4''1Π(R), 3''1Σ''+(R), 2''1Δ(R), 2''1Σ''-(V), 2''1Σ''-(R)) and different molecular orbital (O (1s), Be (1s), O (2s), Be (2s), O (2p)) of non-elastic collision between BeO molecules and low energy electrons (E= 1.0, 2.5, 5.0, 7.5 and 10.0 keV) have been calculated by mathematical modeling on the basis of Math cad program using one fold collision, stepping, Monte-Carlo methods. Initial electrons and their new-generation d-electrons lose some of their energy in each non-elastic collision and this process has been continued until the energy of all generation electrons creates non-elastic collision again. It has been used differential equation of ''dependence of effective cross section of collision on transmitted energy'', which corresponds to the experimental values in these systems and suggested by Gryzinski for electron-electron interaction.
[en] Ab initio molecular orbital (MO) methods are used to provide accurate descriptions of potential energy surfaces for chemical reactions. Thus, far, this has been limited with respect to systems having four or more atoms. However, computer calculation of the energy gradiant with respect to nuclear coordinates is now coming into use. In this review, the analytical calculation of the energy gradient is summarized. The methods of determining geometries, force constants, and normal vibrations for both equilibrium configurations and saddle points are discussed. The intrinsic reaction coordinate is also calculated. Examples of calculations are given
[en] Highlights: • Molecule devices with different lateral linking groups are proposed. • Switching behavior and negative differential resistance are observed. • The switching mechanism with different lateral linking groups is discussed by the molecular orbital.
[en] The crystalline orbital--NDO method is applied to study regular chemisorption of atomic hydrogen on a graphite monolayer, in the 1:1 hydrogen--carbon atomic ratio. Relaxation of the adsorbent is taken into account. The energy band structure shows that the phase produced by chemisorption is an insulator. Population analysis and mapping of the electron density in real space reveals a direct bond established between each hydrogen atom and the underlying carbon atom. This picture is confirmed when examining the total and projected densities of states
[en] Highlights: • Analytic Hessian for large open-shell systems is developed. • IR and Raman spectra can be computed for multiple radical systems. • The fragment molecular orbital method is validated for lipids. • The energetics of hydrogen abstraction reactions in a typical lipid are studied. To quantify the thermodynamics for hydrogen abstraction lipids, the fragment molecular orbital method (FMO) is used to calculate structures and energies of the reactants and products. The analytic second derivative is developed for the open-shell Hartree–Fock formulation of FMO and used to calculate zero point energy corrections. The accuracy of FMO is evaluated for a lipid model and the errors in reaction energies are found not to exceed 0.5 kcal/mol. The reaction energies determined for multiple sites in two lipids are used to discuss likely sites and pathways of radical initiation in membranes.
[en] Highlights: • Generating (5,0) and (6,0) nanotubes series via circumscribing. • Eigenvalues via mirror-plane scission and embedding to produce smaller molecular graphs from larger ones. • Molecular graphs with 2-fold symmetry have two-thirds eigenvalues that are doubly degenerate. • Right-hand mirror-plane fragments contain one set of the doubly degenerate eigenvalues. • Recursion equations for characteristic polynomials for polyynes and quinododimethides. A method for quickly calculating the Hückel molecular orbital eigenvalues and other properties of two series of open-ended single-walled nanotubes is given. Circumscribing generates series of related nanotubes and mirror-plane fragmentation and embedding of larger molecular graphs gives smaller subgraphs resulting in substantial simplification of eigenvalue calculations. Molecular graphs with greater than two-fold symmetry are at least doubly degenerate in about two-thirds of their Hückel molecular orbital eigenvalues and that the right-hand mirror-plane subgraphs only contains one set of these doubly degenerate eigenvalues. Recursion equations derived for the (5,0) nanotube series allow one to obtain eigensolutions for indefinitely large members.
[en] According to molecular orbital theory, the lowest lying acceptor orbital of a methyl group is CH antibonding. It follows, therefore, that transfer of electron density into the group will lead to a weakening of its CH linkages. A like result derives from resonance arguments, H3C-X- reversible H2C(H-)=X reversible, etc., and has been aptly termed ''negative hyperconjugation.'' The observation of significant β-deuterium isotope effects for the gas phase ion-molecule equilibria has recently been cited as evidence for such an effect. We now present theoretical results based on ab initio molecular orbital calculations which further support such an interpretation
[en] The charge transfer (CT) interaction, the most time-consuming term in the general effective fragment potential method, is made much more computationally efficient. This is accomplished by the projection of the quasiatomic minimal-basis-set orbitals (QUAMBOs) as the atomic basis onto the self-consistent field virtual molecular orbital (MO) space to select a subspace of the full virtual space called the valence virtual space. The diagonalization of the Fock matrix in terms of QUAMBOs recovers the canonical occupied orbitals and, more importantly, gives rise to the valence virtual orbitals (VVOs). The CT energies obtained using VVOs are generally as accurate as those obtained with the full virtual space canonical MOs because the QUAMBOs span the valence part of the virtual space, which can generally be regarded as “chemically important.” The number of QUAMBOs is the same as the number of minimal-basis MOs of a molecule. Therefore, the number of VVOs is significantly smaller than the number of canonical virtual MOs, especially for large atomic basis sets. This leads to a dramatic decrease in the computational cost