Quantum molecular dynamics

Electron or ion dynamics are treated using spin‐dependent quantum trajectories. These trajectories are inferred from the Dirac current, which contributes Schroedinger's current and additional spin‐dependent terms, all of which are of order c⁰ in the nonrelativistic regime of particle velocity, where c is the speed of light. The many‐body problem is treated precisely as in classical dynamics. Each electron or ion has its own equation of motion, which is the time‐dependent Dirac or the time‐dependent Schroedinger equation in the relativistic or nonrelativistic regime of particle velocity, respectively. As an example the theory is applied to the electronic structure of the helium atom, in which two electrons with opposite spin states are shown to correlate such that their quantum trajectories keep them on average on opposite sides of the nucleus. As the theory is time dependent, excited states are also generated. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Calculation of the electronic structures of benzimidazole,perimidine, and 5H-dibenzo[d,f]-l,3-diazepine with the inclusion of all of the valence electrons

The distributions of the and charges in benzimidazole, perimidine, and 5H-dibenzo[d,f]-1,3-diazepine molecules, as well as several other characteristics of these compounds, were calculated by the SCF LCAO MO method with the inclusion of all of the valence electrons using the approximation of complete neglect of differential overlap (CNDO). In accordance with the calculations carried out using the -electron approximation, this method predicts increased basicity and nucleophilicity in this series of compounds. It was demonstrated that the mechanism for the development of a positive charge on the meso carbon atom is substantially different for these compounds.Translated from Khimiya Geterotsiklieheskikh Soedinenii, No. 11, pp. 1552–1555, November, 1971     

Pairing theorem for π-electron carbenes

The pairing theorem is proved for planar carbenes formally generated by removing a proton or hydride ion from alternant hydrocarbons, and having identical structure and multiplicity, opposite charges, and different states (² or ²) of the carbene carbon atom. According to this theorem, the elements of the bond-order/residual-charge matrix between different alternant sets coincide with each other, but those between identical sets have opposite signs; for elements of the spin-density matrix, the relationship is the reverse. For such carbenes, this leads to coincidence of the singlet-singlet and singlet-triplet transition energies, electric polarizabilities, conjugation energies, -electron ring currents, diamagnetic susceptibilities, and current contributions to chemical shifts, whereas the charge contributions to the chemical shifts have opposite signs.Donbass State Academy of Construction and Architecture, 1 Derzhavin Street, Makeevka 339023, Donetsk Oblast, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 3, pp. 147–152, May–June, 1996. Original article submitted December 16, 1994.     

“Atomic Bremsstrahlung”: Retrospectives,current status and perspectives

We describe here the “Atomic bremsstrahlung” (AB)—emission of continuous spectrum electromagnetic radiation, which is generated in collisions of particles that have internal deformable structure that includes positively and negatively charged constituents. The deformation of one or both colliding partners induces multiple, mainly dipole, time-dependent electrical moments that become a source of radiation. The history of AB invention is presented and its unusual in comparison to ordinary bremsstrahlung (OB) properties, are discussed. As examples, fast electron atom, non-relativistic and relativistic collisions are considered. Attention is given to ion–atom and atom–atom collisions. Specifics of “elastic” and “inelastic” (i.e. radiation accompanied by destruction of collision partners) AB will be mentioned. Attention will be given to possible manifestation of AB in nature and in some exotic systems, for instance scattering of electrons upon muonic hydrogen. Some cooperative effects connected to AB will be considered. New classical schemes similar to AB will be presented.     

Water-activated cellulose-based electrorheological fluids

The performance of electrorheological (ER) fluids containing cellulose particles dispersed in lubricating oil was investigated as a function of particle water content, DC electric field strength, particle concentration, and temperature. Over a range of applied electric fields (0–3 kV/mm), yield stress was observed to increase with increasing cellulose moisture content up to 8.5 wt% followed by a decrease. Water adsorbed by cellulose particles used in these systems was shown to be non-freezing bound water. The maximum ER response for a cellulose-based fluid at 25 °C was observed at a moisture content near the transition of less mobile liquid-like (LM) water to more mobile liquid-like (MM) non-freezing water. At a constant moisture level, yield stress increased linearly with increases in either electrical field strength or particle concentration, while the ER effect decreased with increasing temperature. The present study concludes that the performance of water-activated ER fluids based on cellulose particles is influenced strongly by the mobility of non-freezing bound water adsorbed onto cellulose.     

Electron and positron atomic elastic scattering cross sections

A method was developed to calculate the total and differential elastic-scattering cross sections for incident electrons and positrons in the energy range from $\text{0.01}\text{eV}$ to $\text{1}\text{MeV}$ for atoms of Z=1–100. For electrons, hydrogen, helium, nitrogen, oxygen, krypton, and xenon, and for positrons, helium, neon, and argon atoms were considered for comparison with experimental data.First, the variationally optimized atomic static potentials were calculated for each atom by solving the Dirac equations for bound electron states. Second, the Dirac equations for a free electron or positron are solved for an atom using the previously calculated static potential accomplished (in the case of electrons) by “adjusted” Hara's exchange potential for a free-state particle. Additional to the exchange effects, the charge cloud polarization effects are considered applying the correlation-polarization potential of O'Connell and Lane (with correction of Padial and Norcross) for incident electrons, and of Jain for incident positrons.The total, cutoff and differential elastic-scattering cross sections are calculated for incident electrons and positrons with the help of the relativistic partial wave analysis. The solid state effects for scattering in solids are described by means of a muffin-tin model, i.e. the potentials of neighboring atoms are superpositioned in such a way that the resulting potential and its derivative are zero in the middle distance between the atoms. The potential of isolated atom is calculated up to the radius at which the long-range polarization potential becomes a value of −10⁻⁸.     

A unified theory of spin 0 nuclear interactions

A Gauge Theory that contains the pion triplet as strong force quanta, a quantum theory of gravity and unifies the strong (nuclear) and gravitational interactions is proposed under a relaxation of the requirement of covariance for Lorentz boost transformations. A modified form of local gauge invariance in which the nucleon field phase is allowed to vary with each time point but not each space point leads to the introduction of a new compensatory field. The quanta of this field are massless spin 0 particles that propagate at the speed of light. They are interpreted as gravitons which mediate the Newtonian gravitational force. It is suggested that the universality of the interaction is linked with the conservation of mass. The associated equation of motion yields Newton's Inverse Square Law for the static case and, because of retardation of potentials, gives rise to a precession of planetary orbits. A qualitative indication of the energy loss observed in the binary pulsar PSR1913+16 within the Newtonian framework is also given. A modification of the Yang–Mills invariance is applied to nucleons. It requires the strong interaction between nucleons to be invariant under independent rotations of the isotopic spin at each time point but not each space point. This results in the introduction of a triplet of compensating fields having massless spin 0 quanta that are interpreted as massless pions. An SU(2)×U(1) theory combining isotopic spin and hypermass symmetries is then developed. Spontaneous Symmetry Breaking yields three massive particles (along with a Higgs particle) and one massless particle. The three massive particles have mass, spin and charge that identify them as pions, while the single massless spin 0 particle, which couples to the nucleons with a strength proportional to mass, is interpreted as the spin 0 graviton. The model provides a resolution of one of the outstanding puzzles of theoretical physics: why gravity is so much weaker than the other forces of nature.     

Dependence of the δ31P chemical shift on the electronic and stereochemical structure of compounds of tricoordinated phosphorus

The trends in the variation of the paramagnetic component p^p of the magnetic screening constant of the ³¹p nucleus with variation in the electronic and stereochemical structure of the compounds of tricoordinated phosphorus are examined on the basis of the concepts of perturbation theory. The dependence of p^p on the bond angle at the phosphorus atom in symmetrically substituted phosphines PM₃, on the electronegativity of the substituents M, and on the resonance integral of interaction in the a bonds of the phosphorus atom was investigated. The nature of the ³¹P chemical shift in the transition from phosphines PM₃ to symmetrical phosphonium salts P⁺M₄, and the role of the unshared electron pair of the phosphorus atom in the screening of its nucleus are examined.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 4, pp. 419–426, July–August, 1986.     

The detachment of nylon particles from quartz plate by electro-osmotic flow

The direct application of electrokinetic phenomena to detergency was investigated. Experiments were carried out to remove particles from substrate by electro-osmosis. A model system which consisted of spherical nylon particles of 5m in mean diameter, a quartz plate, and wash liquid were used in analyzing the kinetic process of particle removal from substrate. When an electric field was applied to the system, electro-osmotic flow took place, and hence the particles were removed from the quartz surface. The -potentials of nylon particles and quartz plate were measured by electrophoresis. The rate constants of removal,, were obtained from the changes with time in the ratio of particle residue by applying the first-order reaction scheme. The value of increased with increasing electric field and with increasing concentration of surfactant. The total force of interaction between particle and plate was calculated on the basis of heterocoagulation theory of colloid stability.It was found from results thus obtained that the hydrodynamic force due to the electro-osmotic flow worked effectively as a mechanical force on the removal process and the adhesion force of particle to substrate reduced by adding surfactant.     

Two-Temperature Transport Coefficients in Argon–Hydrogen Plasmas—I: Elastic Processes and Collision Integrals

The calculation of two-temperature transport coefficients in an argon–hydrogen plasma at atmospheric pressure is performed using a new theory of two-temperature transport properties recently presented. The latter takes into account the coupling between electrons and heavy species, coupling neglected in the already existing theories of Devoto and Bonnefoi. Transport coefficients are calculated at two-temperatures, the kinetic temperature of electrons T_e being different from that of heavy species T_h. This paper is divided into two parts. The first one is related to elastic processes and its aim is to compare the results obtained with this new theory for viscosity , translational thermal conductivities ^tr _e and ^tr _h and electrical conductivity with the previous results of Bonnefoi. The composition is calculated with the modified equilibrium constant of van de Sanden et al. and the most recent interaction potential are discussed. As it could be expected the electron translational thermal conductivity and the electrical conductivity calculated when taking into account or not the coupling between electrons and heavy species show non-negligible discrepancies. Besides this comparison, the results also show the drastic influence of the non-equilibrium parameter =T_e/T_h on the values of , , ^tr _e, and ^tr _h.     

Thermophoretic force on a metallic or nonmetallic particle immersed into a rarefied Plasma

Analytical results of the thermophoretic force on a metallic or nonmetallic spherical particle immersed into a rarefied plasma with a heat flux within the plasma are presented for the extreme case of free-molecule regime and thin plasma sheath. It has been shown that the thermophoresis is predominantly caused by atoms at low plasma temperatures with negligible gas ionization, while it is mainly due to ions and electrons at high plasma temperatures with great degree of ionization. The ion flux incident to a particle is constant on the whole sphere surface, while the electron flux to the metallic sphere is dependent on the -position with slightly greater value at the fore stagnation point. Consequently, there is a small difference between the metallic and nonmetallic spheres in their -distributions of the floating potential on the surface, which causes the thermophoretic force on a nonmetallic sphere to be appreciably greater than that on a metallic sphere at high plasma temperatures. Expressions for the total thermophoretic force on a metallic sphere and its components due to, respectively, atoms, ions, and electrons have been given in a closed form. Calculated results are also presented on the effects of pressure and of electron/heavy-particle temperature ratio. These results can be understood based on the variation of atom, ion, and electron thermal conductivities with the gas pressure, the temperature, and the temperature ratio.     

Two-Temperature Transport Coefficients in Argon–Hydrogen Plasmas—II: Inelastic Processes and Influence of Composition

Recently, a two-temperature transport properties theory has been proposed that retains the coupling between electrons and heavy species in thermal plasmas where the kinetic temperature of electrons Te can be different from that of heavy species Th. This paper is devoted to the application of this approach to an argon–hydrogen mixture at atmospheric pressure, taking into account inelastic processes and considering chemical equilibrium. In this second part are studied: the development of a new method to calculate the reaction thermal conductivity (inelastic collisions) in a non-equilibrium (two-temperature) plasma taking into account the coupling between electrons and heavy species; the influence of the composition calculation methods comparing the modified equilibrium constant method used in part 1 to the stationary kinetic calculation one; the influence on the transport properties (, , ) of the composition calculation method and non-equilibrium parameter =T_e/T_h.The different plasma compositions obtained either through an equilibrium constant or a stationary kinetic method are first compared and, for example, for =1.6, a discontinuity at T_e=11,000 K and an ionization delay are observed in stationary kinetic calculation, relative to the equilibrium constant method. Electrical conductivity, viscosity as well as thermal conductivity, including the translational, internal and reactional contributions, are calculated up to 25,000 K. It is shown that the plasma composition has a strong influence on transport coefficients, inducing shifts or discontinuities in the curves of transport coefficients, depending on the chosen method of calculation.     

The relationship between electronic charges and lengths of σ-bonds

Summary A dependence was shown to exist between the electronic charges and the lengths of -bonds of a saturated carbon atom, which permitted us to explain and to correct the existing data on interatomic distances.     

Electronic and geometric structure of the complex FeN2

The extended Hückel method has been used to calculate the electronic structure of linear and perpendicular complexes of the Fe atom with the N₂ molecule. The linear complex is found to be more stable, in agreement with the small amount of available experimental data. Its stabilization is due to the combined action of two effects-promotion of electrons in the -core of the complex in the direction of the Fe atom, and promotion in the -cloud in the opposite direction. In the perpendicular complex, the last effect is almost absent because of t the antibonding nature of the -bonds, and this explains its lower stability.The authors thank G. I. Kagan for providing the EH program.     

Spectroscopic and quantum-chemical study of 5-alkoxypyridine-2- and 6-alkoxypyridine-3-carboxylic acids

The peculiarities of the structures of 5-alkoxypyridine-2- and 6-alkoxypyridine-3-carboxylic acids were studyed by experimental (IR, UV, and PMR spectroscopy) and quantum-chemical methods. It was established that both types of compounds exist in the form of dimers in the crystalline state, whereas in CC1₄, the first type exist in the form of monomers, while the second type exist in the form of dimers and monomers in dynamic equilibrium. The ability to form an intramolecular hydrogen bond and the interaction of the unshared pairs of electrons of the ring nitrogen atom and the oxygen atom of the C=0 group are among the reasons for the absence of liquid-crystal properties in 5-alkoxypyridine-2-carboxylic acids as compared with 6-alkoxypyridine-3-carboxylic acids, which have such properties. From the point of view of the electronic structures, 6-alkoxypyridine-3-carboxylic acids differ from 5-alkoxypyridine-2-carboxylic acids in that in the former the ring nitrogen atom and the COOH and OAlk groups have an identical effect on the sign of the -electron charges of the ring carbon atoms, and their -dipole moments are directed virtually along the longitudinal axis of the molecule.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 228–234, February, 1978.     

Perturbation energy expansions based on two-component relativistic Hamiltonians

The approximate elimination of the small-component approach provides ansätze for the relativistic wave function. The assumed form of the small component of the wave function in combination with the Dirac equation define transformed but exact Dirac equations. The present derivation yields a family of two-component relativistic Hamiltonians which can be used as zeroth-order approximation to the Dirac equation. The operator difference between the Dirac and the two-component relativistic Hamiltonians can be used as a perturbation operator. The first-order perturbation energy corrections have been obtained from a direct perturbation theory scheme based on these two-component relativistic Hamiltonians. At the two-component relativistic level, the errors of the relativistic correction to the energies are proportional to ⁴ Z ⁴, whereas for the relativistic energy corrections including the first-order perturbation theory contributions, the errors are of the order of ⁶ Z ⁶–⁸ Z ⁸ depending on the zeroth-order Hamiltonian.Contribution to the Björn Roos Honorary Issue     

原子构造原理与过渡元素原子的价电子组态

众所周知,元素周期系过渡元素基态原子价电子组态的多样化是已往的原子构造理论无论是从定性还是从定量方面都是迄今难以给出圆满理论解释的原子构造现象之一^[1-11]。本文介绍新近提出的原子构造的对称性原理以及依据这一原理对上述原子构造现象所作的系统理论解释。     

Relativistic perturbation theory of molecular structure

Summary The recently developed relativistic double perturbation theory is extended to handle relativistic changes of molecular structure more easily. This is achieved by simple coordinate scalings. Accurate higher order mixed perturbation energies for H ₂ ⁺ are calculated. The relativistic changes of bond energy,DE, of bond length,R _e , and especially of force constant,k, and of anharmonicity,a, are large, up to 100%·(Z/c)². The dominant contributions tok anda are due to the indirect change of the nonrelativistick anda connected with the relativistic change of bond length. Accordingly the relativistic changes obey Badger's and Gordy's rules (–RDEk).Dedicated to Prof. Klaus Ruedenberg in appreciation of his fundamental contributions to both formal theory and physical explanations in quantum chemistry     

Kinetics of vinyl acetate emulsion polymerization

The emulsion polymerization of vinyl acetate has generally been considered a special type of reaction that is not covered by the Smith-Ewart theory. Although the number of particles depends on coalescence rates and can not be predicted by this theory, the polymerization rate data are consistent with the general concepts of Smith and Ewart, including reaction primarily inside swollen polymer particles, escape of radicals from particles, and termination of chains inside the particles. Allowing for rapid exchange of radicals following chain transfer leads to a simple equation which fits much of the published data for cases of both very low and very high values of n , the average number of radicals per particle.