Sigma trans promotion effect in transition metal complexes: a manifestation of the composite nature of binding energy

It is well known that intra-fragment electronic reorganization is one among several important components of the binding energy (bond dissociation energy) for two fragments forming an adduct. An interesting manifestation of this notion is proposed: a counterintuitive trend in binding energies that shall be commonly observed for a series of particular open shell transition metal containing complexes binding a small molecule at an empty coordination site. The prediction is that stronger σ interaction between the metal and the ligand trans to the empty site will result in a larger magnitude of binding energy and, possibly, a lower substrate coordination barrier. This trend, which we call the ‘trans promotion effect’ (TPE), is exemplified with a case study of dinitrogen binding by tri- and four-coordinated Mo(III) complexes. It is demonstrated that a trans amine ligand significantly increases the magnitude of dinitrogen binding energy. Orbital analysis and decomposition of the binding energy show that substrate coordination is favoured by stronger interaction of Mo with the trans ligand due to the d_z2 orbital of Mo that is occupied in the complex but vacant in the dinitrogen adduct.     

Bound polaron in a wurtzite GaN/AlxGa1 − xN ellipsoidal finite-potential quantum dot

A variational method is used to study the ground state of a bound polaron in a weakly oblate wurtzite GaN/Al_xGa_1 − xN ellipsoidal quantum dot. The binding energy of the bound polaron is calculated by taking the electron couples with both branches of LO-like and TO-like phonons due to the anisotropic effect into account. The interaction between impurity and phonons has also been considered to obtain the binding energy of a bound polaron. The results show that the binding energy of bound polaron reaches a peak value as the quantum dot radius increases and then diminishes for the finite potential well. We found that the binding energy of bound polaron is reduced by the phonons effect on the impurity states, the contribution of LO-like phonon to the binding energy is dominant, the anisotropic angle and ellipticity influence on the binding energy are small.     

Interaction between two hydrogen atoms approaching a metal surface

Two regimes of HH interaction outside a metal surface are considered: (i) Beyond the spill-out region of the metal electrons (physisorption) (ii) Embedded protons in the electron spill-out. Using an extension of the Heitier-London model to treat (i), the H₂ binding energy for the molecule parallel to the surface is reduced, whereas for the perpendicular configuration stronger binding obtains. In (ii), the asymptotic form of the screening charge round a single proton is considered, in a linear response framework, and for an infinite barrier model of the surface. If the screened potential has no singularities in k space, then the interaction energy ΔE(X), X being the distance between the protons, falls off as X^?5 times an oscillatory function, for H₂ parallel to the planar metal surface. The effect of self-consistency on this result is then examined and it is concluded that the asymptotic interaction energy is unchanged in form, though the amplitude is altered.     

The polaron effect on the binding energy of a shallow donor impurity in quantum-well wires in an electric field

Using a variational technique, the effect of electron-longitudinal optical (LO) phonon interaction on the ground and the first few excited states of a hydrogenic impurity in a semiconductor quantum wire of rectangular cross section under an external electric field is studied theoretically for the impurity atom doped at various positions. The results for the binding energy as well as polaronic correction are obtained as a function of the size of the wire, the applied uniform electric field and the position of the impurity. It is found that the presence of optical phonons changes significantly the values of the impurity binding energies of the system. Taking into account the electron–LO phonon interaction the 1s→2p_y and 1s→2p_z transition energies are calculated as a function of applied electric field for different impurity positions.     

Effect of dipole forces on the structure of the liquid phases of DNA

The dipole-dipole contribution to the energy of the pair interaction between DNA molecules has been calculated and analyzed. Rigid fragments of DNA, i.e., of a length of about the persistent length, which have discrete dipole moments of base pairs, are considered. For a given distance between the centers of mass of molecules, the energy of the dipole-dipole interaction is a function of three angular variables; the angles ?₁ and ?₂ between the central dipoles of both molecules and the z axis passing through the centers of the molecules, as well as the angle ξ between long axes of the molecules, are taken as these variables. It is shown that the dipole energy has minima when the mutual orientation of the molecules satisfies one of the following conditions: (i) ?₁ = ?₂ = 0 or (ii) ?₁ = ?₂ = π. The cholesteric twist angle ξ can be both positive and negative in dependence on the type of the minimum. For realistic cholesteric dispersion parameters, the dipole energy is only slightly lower than the experimentally known binding energy of the molecules in dispersion. The results allow the assumption that the dipole forces significantly affect the structure and other properties of DNA suspensions; in particular, they can lead to nontrivial texture phenomena, biaxial correlation, and multistability.     

Effects of electron–phonon interaction and impurity on optical properties of hexagonal-shaped quantum wires

We have investigated the influence of electron–phonon (e–p) interaction and hydrogenic donor impurity simultaneously on energy difference, binding energy, the linear, nonlinear and total refractive index changes and absorption coefficients of a hexagonal-shaped quantum wire. For this goal, we have used finite-element method (FEM), a compact density matrix approach and an iterative procedure. It is deduced that energy difference and binding energy decrease by changing the impurity position with and without e–p interaction. The dipole matrix elements have complex behaviours in the presence of impurity with and without e–p interaction. The refractive index changes and absorption coefficients increase and shift towards lower energies by enhancing a ₁ with central impurity. In the presence of central impurity, the absorption coefficients and refractive index changes enhance and shift toward higher energies when e–p interaction is considered.     

Phonon and electron-hole plasma effects on binding energies of excitons in wurtzite GaN/In<Subscript>x</Subscript>Ga<Subscript>1−x</Subscript>N quantum wells

The binding energy of an exciton screened by the electron-hole plasma in a wurtzite GaN/In _x Ga_1−x N quantum well (in the case of 0.1 < x < 1 within which the interface phonon modes play a dominant role) is calculated including the exciton-phonon interaction by a variational method combined with a self-consistent procedure. The coupling between the exciton and various longitudinal-like optical phonon modes is considered to demonstrate the polaronic effect which strongly depends on the exciton wave function. All of the built-in electric field, the exciton-phonon interaction and the electron-hole plasma weaken the Coulomb coupling between an electron and a hole to reduce the binding energy since the former separates the wave functions of the electron and hole in the z direction and the later two enlarge the exciton Bohr radius. The electron-hole plasma not only restrains the built-in electric field, but also reduces the polaronic effect to the binding energy.     

Study of the Interaction of Fangchinoline with Human Serum Albumin by Fluorescence and UV Spectroscopic Method

The interaction of fangchinoline with human serum albumin (HSA) was studied by use of fluorescence quenching spectra, synchronous fluorescence spectra, and ultraviolet spectra. It was shown that fangchinoline has a strong ability to quench the fluorescence of HSA. The Stern‐Volmer curves based on the quenching of the fluorescence of HSA by fangchinoline indicated that the quenching mechanism of fangchinoline on HSA was static quenching and non‐radiation energy transfer. Based on the Förster theory of non‐radiation energy transfer, the binding distances (r) and the binding constants (K _A) between fangchinoline and HSA were found. The thermodynamic parameters obtained revealed that the interaction between fangchinoline and HSA was mainly driven by hydrophobic force. The conformational changes of HSA were investigated by use of synchronous fluorescence. The result indicates that an ionic electrostatic interaction between fangchinoline and HSA could not be excluded.     

Interaction of moderately reactive molecules with organic superhalogens: a theoretical perspective

The interaction of four moderately reactive molecules (MRMs), benzene (BZ), water, ammonia and silicon dioxide, with three aromatic organic superhalogens (OSHs) has been investigated at the density functional theory (DFT) level. The strength of the interaction is analysed from the distortions in the structures of both the MRMs and OSHs after complexation and the calculated binding energy (BE) values between the two interacting moieties. The interaction becomes stronger as we move from BZ to H₂O to NH₃ and strongest for SiO₂ molecule. Contributions from different terms in total interaction energy have been examined by energy decomposition analysis (EDA). The charge flow values between MRMs and OSHs, and Mulliken spin density localised on the moderately reactive molecules have been evaluated to ensure whether the interaction is ionic or not. Atoms in Molecules (AIM) analysis has been performed to characterise the bonds formed between the two. Overall, our study gives a comprehensive account of the interaction between the moderately reactive molecules and three theoretically designed aromatic organic superhalogens, which will further motivate researchers in the field of superhalogen chemistry.     

On the encapsulation of azafullerenes inside the single-walled carbon nanotubes: Density-functional theory based treatments

We theoretically studied the encapsulation of azafullerene (C₅₉N) inside the single-walled carbon nanotubes (SWCNTs) from the first-principles. Adsorption energy is calculated, and the azafullerene affinities for the typical semiconducting and metallic nanotubes are investigated and compared with those of pure C₆₀ fullerene. It has been found that the azafullerene as well as the fullerene affinity for the semiconducting nanotubes is stronger than that for the metallic ones, and the energy values and binding distances are typical for the physisorption. Our first-principles results indicate that the interaction between SWCNTs and azafullerenes is comparable with the nanotubes-C₆₀ system. The charge analysis shows, however, that the charges have been transferred from the cage to the tube in the azafullerene peapods, while in the fullerene peapods the charges were found to be transferred from the tube to the fullerene nanocage. Furthermore, it was found that the interaction between the considered fullerenes and host nanotubes strongly depends on the tube diameters.     

Electron pairing by cooperation of superexchange and polaron effects

This paper proposes a pairing mechanism relevant to high T_c superconductors with strong electron correlations. The Hubbard model is extended to account for a large electron-phonon interaction. It is shown that the band width is much reduced by the polaron effect, but that the superexchange interaction is not reduced. The cooperation of superexchange and polaron effects makes an anisotropic singlet pair a stable bound state, with the largest binding energy in the one-dimensional system.     

XPS and XAES study of the interaction of palladium and copper overlayers with fullerene films

X-ray photoelectron and Auger spectroscopies were used to examine surface bonding and overlayer growth during palladium and copper deposition onto films of fullerene, C₆₀ The results were consistent with metal cluster formation on C₆₀. The observed positive core electron binding energy shifts in small metallic clusters supported on C₆₀ were shown to originate in metal-fullerene interaction accompanied by charge transfer. Palladium-fullerene intermixing at temperatures as low as ss 50°C was observed for small Pd coverages.     

非对称方势阱中的激子及其与声子的相互作用

采用类LLP(Lee-Low-Pines)变换和分数维变分法,在讨论有限深非对称方势阱Ga_1－xAl_xAs/ GaAs/Ga_0.7Al_0.3As的分数维基础上,计算了其中激子的基态能量以及声子对其影响,随着势阱宽度增加,激子能量先减小后增大,出现一个最小值.讨论了一侧势垒高度变化对分数维、激子基态能量的影响,并发现声子作用使得激子能量明显增大.另外,非对称方势阱中的激子结合能随阱宽的减小而增     

Strong influence of defects on the electronic structure of Pt adatoms and clusters on graphite

We study the specific impact of defects such as step edges at the graphite surface on the electronic configuration of adsorbed Pt atoms and Pt₈ clusters. Surface diffusion is strongly reduced by depositing Pt and Pt₈ into a thin rare gas layer. In this configuration a very narrow adatom Pt 4f spectrum is found at an exceptionally small binding energy, similar to Pt surfaces. Both, adatom and cluster spectra are strongly shifted towards higher binding energy when allowed to diffuse towards defects like step edges. The strong shifts are indicative of a chemical reaction at the step edges and are conjectured to be part of the particle size dependent binding energy shifts typically observed for transition metal clusters grown on the surface of graphite.     

Modeling nanoparticle uptake and intracellular distribution using stochastic process algebras

Intermolecular energy decomposition analysis (EDA) is reported for the binding of CO₂ with zeolitic imidazole frameworks (ZIF) to provide a molecular level interpretation of the recent capacity and selectivity measurements of several ZIFs and to suggest a theoretical guideline to improve their performance further, using 1?nm size of organic linker fragment of the ZIFs as a target molecule. The EDA suggests that the local electronic interaction of CO₂ and the substituent groups, mainly frozen density and polarization interactions with little charge transfer, is the primary binding interaction, but the electron correlation effects can be equally or more important depending on the binding geometry and functional groups. The present correlated calculations identify the preferred ZIF binding sites for various gases including CO₂ to be mostly near the benzene substituent groups rather than the plane of imidazole rings. We predict that the NH₂-substituted ZIF would have an enhanced capacity of CO₂ as compared to the NO₂-substituted ZIF that was recently synthesized and reported to be one of the materials with the best capacity results along with high gas selectivity. The present calculations may imply that the local functionality of the linking organics, rather than detailed framework structures, may be of primary importance in designing certain high capacity MOF or ZIF materials.     

Neutron Matter Properties Using Skyrme Interaction

The purpose of the present work is to extend earlier nuclear matter calculations to study the properties of neutron matter. The binding energy per particle, symmetry energy, single particle potential, effective mass, and magnetic susceptibility are calculated using a modified Skyrme interaction. These are calculated as a function of the Fermi momentum k_f in the range 0 < k_f < 2 fm^?1. Two sets of the interaction parameters are obtained by fitting the interaction parameters using the available information on neutron matter. Relativistic corrections to the order 1/c² are also calculated. The relativistic corrections are very small and they increase as k_f is increased.     

Magnetic impurity interactions in a quantum well on the base of IV-VI semiconductors

We study the indirect exchange interaction of magnetic impurities via 2D excitations in a quantum well on the base of IV-VI narrow-gap semiconductors. The energy spectrum of 2D excitations takes into account the nonparabolicity of dispersion as well as the strong spin-orbit interaction. The calculations are performed for the case when the main mechanism is an exchange by virtual electron-hole pairs. It means that we assume the Fermi level to lie inside the energy gap, and the temperature to be small, T << ϵ₀. It is shown that at large distances. R >> ν/ϵ₀ (2ϵ₀ is the excitation energy for nearest size-quantized subbands, ϵ the interband interaction parameter), the antiferromagnetic interaction of pairs dominates, so that the impurity spins tend to be directed along the heterojunction plane perpendicular to the vector connecting the impurities. The interaction contains both the Heisenberg and pseudodipole terms.     

The effect of nonparabolicity on binding energy of ground and excited states in a corrugated quantum well

The binding energy of a hydrogenic impurity is calculated in a Ga_1−xAl_xAs/Ga_1−yAl_yAs corrugated quantum well within the single band effective mass approximation for different Al concentration. Binding energy of the ground state and the excited state of a donor is calculated, with the inclusion of 2D Hartree dielectric screening function. The effect of nonparabolicity of the conduction band is considered through the energy dependent effective mass. The effect of nonparabolicity on spin–orbit interaction energy is found. The oscillator strength coupling between the ground state and the excited state is calculated. The dependence of the donor binding energy on the well width and the Al-concentration is discussed. These results are discussed with the available data in the literature.     

Physisorption kinetics of electrons at plasma boundaries

Plasma-boundaries floating in an ionized gas are usually negatively charged. They accumulate electrons more efficiently than ions leading to the formation of a quasi-stationary electron film at the boundaries. We propose to interpret the build-up of surface charges at inert plasma boundaries, where other surface modifications, for instance, implantation of particles and reconstruction or destruction of the surface due to impact of high energy particles can be neglected, as a physisorption process in front of the wall. The electron sticking coefficient s_e and the electron desorption time τ_e, which play an important role in determining the quasi-stationary surface charge, and about which little is empirically and theoretically known, can then be calculated from microscopic models for the electron-wall interaction. Irrespective of the sophistication of the models, the static part of the electron-wall interaction determines the binding energy of the electron, whereas inelastic processes at the wall determine s_e and τ_e. As an illustration, we calculate s_e and τ_e for a metal, using the simplest model in which the static part of the electron-metal interaction is approximated by the classical image potential. Assuming electrons from the plasma to loose (gain) energy at the surface by creating (annihilating) electron-hole pairs in the metal, which is treated as a jellium half-space with an infinitely high workfunction, we obtain s_e≈10^-4 and τ_e≈10^-2 s. The product s_eτ_e≈10^-6 s has the order of magnitude expected from our earlier results for the charge of dust particles in a plasma but individually s_e is unexpectedly small and τ_e is somewhat large. The former is a consequence of the small matrix elements occurring in the simple model while the latter is due to the large binding energy of the electron. More sophisticated theoretical investigations, but also experimental support, are clearly needed because if s_e is indeed as small as our exploratory calculation suggests, it would have severe consequences for the understanding of the formation of surface charges at plasma boundaries. To identify what we believe are key issues of the electronic microphysics at inert plasma boundaries and to inspire other groups to join us on our journey is the purpose of this colloquial presentation.     

Impurity magneto-optical absorption with the participation of resonance states of D 2 − centers in quantum wells

The dependence of the average binding energy of the resonance g-state of a D ₂ ^? center on the induction of an external magnetic field in a quantum well with a parabolic confining potential is studied using the zero-range potential method. It has been shown that with an increasing exchange interaction, the character of the dependence of the average binding energy of the resonance g-state of the D ₂ ^? center on the induction of the external magnetic field changes. It has been assumed that in GaAs/AlGaAs quantum wells alloyed with small Si donors, resonance D ₂ ^? states can exist under conditions of exchange interaction. It has been found that in spectra of impurity magneto-optical absorption in multiwall quantum structures, exchange interaction manifests itself as oscillations of interference origin.