Simplified electrostatic model for the thermodynamic excess potentials of binary strong electrolyte solutions with size-dissimilar ions

Modern theories of electrolyte solutions are physically accurate but difficult to apply for real-life systems; a need therefore exists to theoretically derive simplified and practically useful mathematical expressions for thermodynamic excess functions. This can be done by incorporating ion-size dissimilarity into the classical Debye-Hückel model [Physik Z. 24, 185 (1923)], under conditions at which non-electrostatic contributions are negligible. If the contact distance between the central (β) ion and a cloud (α) ion is a for counter-ions and b for co-ions, two basic cases exist, b < a and b > a. In both, a ‘smaller-ion shell’ (SiS) at the edge of the ionic cloud, bordered by the spherical surfaces of radius b and a, admits only the smaller α ions [Thomlinson and Outhwaite, Mol. Phys. 47, 1113 (1982)]. In the b < a case, the SiS contributes an ionic repulsion effect and the overall extra-electrostatic potential energy, Ψ _{b < a} (κ) ? κ, reciprocal screening length–exhibits a minimum. For b > a, the SiS contributes an ‘extra ionic attraction’ and the overall extra-electrostatic energy, Ψ _{b > a} (κ) declines monotonically with increasing κ. The entire Ψ contribution, Ψ_±, is a linear combination of the Ψs of the two counter β ions. The effectiveness of Ψ_± is demonstrated for real-life electrolyte systems, based on experimental mean ionic activity coefficients and their concentration dependencies. Fitting theory with experiment generates ion-size parameters that represent realistic interionic collision distances in solution, unlike parallel parameters based on other simplified theories.     

Theoretical characterisation of irreversible and reversible hydrogen storage reactions on Ni-doped C60 fullerene

An attempt has been made to characterise the irreversible and reversible hydrogen storage reactions on Ni-doped C₆₀ fullerene by using the state of the art density functional theory calculations. The single Ni atom prefers to bind at the bridge site between two hexagonal rings of C₆₀ fullerene, and can bind up to four hydrogen molecules with average adsorption energies of ?0.85, ?0.83, ?0.58, and ?0.31 eV per hydrogen molecule. No evidence for metal clustering in the ideal circumstances and the hydrogen storage capacity is expected to be as large as 8.9 wt%. While the desorption activation barriers of the complexes nH₂NiC₆₀ (n = 1, 2) are outside the desirable energy window recommended by the department of energy for practical applications (–0.2 to –0.6 eV), the desorption activation barriers of the complexes nH₂NiC₆₀ (n = 3, 4) are inside this window. The irreversible 2H₂ + NiC₆₀ and reversible 3H₂ + NiC₆₀ interactions are characterised in terms of several theoretical parameters such as: (1) densities of states and projected densities of states, (2) pairwise and non-pairwise additivity, (3) infrared, Raman, and proton magnetic resonance spectra, (4) electrophilicity, and (5) statistical thermodynamic stability.     

O2分子激发态a1Δg和b1Σ+g态的分析势能函数

以aug-cc-pVQZ,cc-pV5Z,6-311++g（d,p）和6-311++g（3df,3pd）等为基函数,采用多组态相互作用（MRCI）方法对O₂分子最低的两个激发态¹Δ_g和¹Σ⁺_g的平衡结构、谐振频率和势能曲线进行了计算.并选用Murrell-Sorbie势能函数对曲线进行拟合,利用拟合的参数值计算出了力常数和光谱数据.结果表明计算值与实验值符合较好. 关键词： MRCI 势能函数 力常数 光谱数据     

Computational investigation of hydrogen storage on B5V3

Based on density functional theory method with 6-311+G(d,p) basis set, the structures, stability and hydrogen storage capacity of B₅V₃ have been theoretically investigated. It is found that a maximum of seven hydrogen molecules can be adsorbed on B₅V₃ with gravimetric uptake capacity of 6.39 wt%. The uptake capacity exceeds the target set by the US Department of Energy for vehicular application. Moreover, the average adsorption energy of B₅V₃ 01 (7H₂) is 0.60 eV/H₂ in the desirable range of reversible hydrogen storage. The kinetic stability of H₂ adsorbed on B₅V₃ 01 is confirmed by using gap between highest occupied molecular orbital (HOMO)and the lowest unoccupied molecular orbital (LUMO). The gap value of B₅V₃ 01 (7H₂) is 2.81 eV, which indicates the compound with high stability. In addition, the thermochemistry calculation (Gibbs free energy corrected adsorption energy) is used to analyse if the adsorption is favourable or not at different temperatures. It can be found that the Gibbs corrected adsorption energy of B₅V₃ 01 (7H₂) is still positive at 400 K at 1 atm. It means that the adsorption of seven hydrogen molecules on B₅V₃ 01 is energetically favourable in a fairly wide temperature range. All the results show that B₅V₃ 01 can be considered as a promising material for hydrogen storage.     

On kaonic hydrogen. Phenomenological quantum field theoretic model revisited

We argue that due to isospin and U-spin invariance of strong low-energy interactions the S-wave scattering lengths a ⁰ ₀ and a ¹ ₀ of ˉN scattering with isospin I = 0 and I = 1 satisfy the low-energy theorem a ⁰ ₀ +3a ¹ ₀ = 0 valid to leading order in chiral expansion. In the model of strong low-energy ˉN interactions at threshold (Eur. Phys. J. A 21, 11 (2004)) we revisit the contribution of the Σ(1750) resonance, which does not saturate the low-energy theorem a ⁰ ₀ +3a ¹ ₀ = 0, and replace it by the baryon background with properties of an SU(3) octet. We calculate the S-wave scattering amplitudes of K^-N and K^-d scattering at threshold. We calculate the energy level displacements of the ground states of kaonic hydrogen and deuterium. The result obtained for kaonic hydrogen agrees well with recent experimental data by the DEAR Collaboration. We analyse the cross-sections for elastic and inelastic K^-p scattering for laboratory momenta 70MeV/c < p _K < 150MeV/c of the incident K^--meson. The theoretical results agree with the available experimental data within two standard deviations.     

Calculation of energy characteristics for Si<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>–Si structures with single quantum wells

Energy characteristics of Si_1–x Ge _x –Si quantum-size structures with single quantum wells were calculated numerically based on a four-band k·p method. Analytical expressions for the Luttinger parameters are obtained as functions of the component composition of Si_1–x Ge _x compounds. Analytical expressions for the energy ħω of optical band-to-band transitions are obtained in an effective mass approximation and agree well with numerical calculations by the k·p method. This allows one to determine accurately a range of changes while varying the component compositions and thickness of the active and barrier layers.     

Synthesis,crystal structure and electrical properties of (C5H13NCl)2 SnCl6

In this work, a novel compound Bis(2-chloropropyl-N,N-dimethyl-1-ammonium) hexachloridostannate(IV) was synthesized and characterized by; single X-ray diffraction, Hirshfeld surface analysis, differential scanning calorimetric and dielectric measurement. The crystal structure refinement at room temperature reveled that this later belongs to the monoclinic compound with P2₁/n space group with the following unit cell parameters a = 7.2894(7) Å, b = 12.9351(12) Å, c = 12.2302(13) Å and β = 93.423 (6) °. The structure consists of isolated (SnCl₆)^2? octahedral anions connected together into layers via hydrogen bonds N–H….Cl between the chlorine atoms of the anions and the hydrogen atoms of the NH groups of the [C₅H₁₃NCl]⁺ cations. Hirschfeld surface analysis has been performed to gain insight into the behavior of these interactions. The differential scanning calorimetry spectrum discloses phase transitions at 367 and 376.7 K. The electrical properties of this compound have been measured in the temperature range 300–420 K and the frequency range 209 Hz–5 MHz. The Cole–Cole (Z′ versus Z″) plots are well fitted to an equivalent circuit model. The transition phase observed in the calorimetric study is confirmed by the change as function of temperature of electrical parameter such as the conductivity of grain (σ_g) and the σ_dc.     

Resonance optical spectroscopy of long-period quantum-well structures

Theory of specular light reflection from long-period quantum-well structures taking into account the exciton contribution to dielectric polarization has been developed for an arbitrary relation between the background refractive index in the well, n _a, and barrier-material refractive index nb. General expressions for the optical reflection and transmission coefficients for a structure with N equidistant quantum wells are derived with the use of the Green’s function and transfer matrix methods. Normal and oblique light reflectance spectra from II-VI-based heterostructures were found to reveal a bright interference pattern caused by the difference between n _a and n _b. A comparison of the theory with experiment has yielded the dispersion of n _a and n _b within a broad wavelength range and the parameters of the quasi-two-dimensional heavyhole exciton (e1-hh1), namely, the resonant frequency and the radiative and nonradiative damping rates. Reflectance spectra from resonant Bragg and quasi-Bragg structures with real exciton parameters are calculated, and the effect on these spectra of the refractive-index difference and the deviation from the Bragg condition is analyzed. Fiz. Tverd. Tela (St. Petersburg) 39, 2072–2078 (November 1997)     

Density-functional study of CO adsorbed on RhN （N = 2-19） clusters

We investigate the structural, electronic and adsorption properties of one single CO molecule adsorbed on Rh_N (N = 2-19) clusters, using the density-functional theory in the spin-polarized generalized gradient approximation. It is found that the structural growth model of the Rh_N clusters transforms from double layers (N = 12-16) to three layers (N = 17-19). Three different adsorption types are the atop site adsorption for N = 6, 8, 9, 11, 12, the bridge site adsorption for N = 2-5, 7, 10, 13-15, 17 and the face adsorption for N = 16, 18, 19. The adsorption abilities of Rh_N clusters are related to C-O bond length, vibrational frequency, adsorption energy and the charge transfer between CO and Rh clusters as well as the electronic density of state. With the increase of Rh cluster size, the adsorption energy of CO adsorbed on Rh_N clusters tends to be 2.2 eV-2.3 eV, which is 0.2 eV-0.3 eV larger than the theoretical value (about 2.0 eV) of CO molecule adsorption on clean Rh (111) surface.     

Evolution of the structure of Rb2ZnCl4 over the temperature range 4.2–310 K

X-ray diffraction is used to study the temperature dependence of the lattice parameters and the sequence of structural realignments in crystalline Rb₂ZnCl₄ over temperatures of 4.2–310 K. The appearance of and changes in the system of satellite reflexes indicative of structural ordering are studied. Below 74 K, on going into the monoclinic phase (space group A11a), anomalies are observed in the behavior of the lattice parameters, and superstructural reflexes develop with wave vectors q=a ^*/3+b ^*/2+c ^*/2 corresponding to an increase by a large factor in initial parameters a, b, and c of the Pnma-phase. Fiz. Tverd. Tela (St. Petersburg) 41, 1084–1090 (June 1999)     

The relation of chemical potentials and reactivity studied by a state path sum

Exact quantum transition probabilities for collinear F + H₂ → FH + H on two different potential energy surfaces are analyzed in terms of regional effects of the potentials. The potentials considered are (a) a weakly curved rotated harmonic model potential and (b) a strongly curved rotated Morse potential fitted to the ab initio SCFCI surface of Bender et al. In both potentials a, b the energy along the reaction path has the same parameters, and three successive regions 1–3 are analysed. The main results are: (1) at very low total energies the reactants are reflected from the activation barrier (region 1 of potentials a, b). (2) in the downhill region 2 of potentials a and b the molecules are weakly and strongly excited, respectively. Region 2 of the realistic potential b also causes H₂ back reflection, depending on the total energy (although there is no barrier in region 2!); (3) In the final shallow sloped, weakly curved region 3 of potential a, part of the excited molecules are again de-excited before reaching the product's configuration. On the contrary, region 3 of potential b has a non-curved reaction path, and the reaction is adiabatic therein, i.e. the van der Waals minimum is irrelevant for vibrational excitation. Practical aspects of the state path sum method are discussed in detail.     

B（N）掺杂单壁碳纳米管的Al原子吸附性能的第一性原理研究

采用基于密度泛函理论的平面波赝势方法和广义梯度近似,对未掺杂、掺B、掺N的碳纳米管(CNT)不同位置上Al原子的吸附进行了几何优化,计算了吸附Al、掺杂前后CNT的能带结构、态密度、差分电荷密度、电荷布居数和吸附能.计算结果表明,掺B使CNT形成缺电子状态,利于具有自由电子的Al原子的吸附结合,可显著提高Al在金属性的(5,5)CNT和半导性的(8,0)CNT外壁的吸附能;掺杂N形成多电子状态,在费米能级附近半满的施主能级也利于填充Al的价电子,改善Al在(5,5)CNT和(8,0)CNT外壁的吸附结合性 关键词： 密度泛函理论 单壁碳纳米管 B(N)掺杂 Al原子吸附     

Hydrogen in amorphous and crystalline ytterbium films

Ytterbium vapor condensation on a liquid-helium cooled substrate in a hydrogen atmosphere is used to obtain Yb-H films containing up to 55 at.% hydrogen. Various thermodynamic and kinetic parameters of the transition of these films from the amorphous to the crystalline state (a→c transition) are investigated along with the electrical conductivity of these states. It is shown that the investigated properties of Yb-H films containing up to 40 at.% hydrogen are essentially indistinguishable from those of pure Yb films in the temperature interval 4.2–293 K. Increasing the hydrogen concentration to 55 at.% leads to an insignificant increase in the electrical resistivity, the kinetic temperature, and the activation energy of the a→c transition, and also to a decrease of the propagation speed of self-maintaining avalanche (explosive) crystallization. Reasons for the observed influence of hydrogen on the properties of Yb-H films are analyzed. The examined low-temperature Yb-H condensates can be characterized as a “frozen” solid solution of hydrogen in ytterbium in the temperature interval 4.2–293 K. Storing such films at room temperature leads to the formation of ionic ytterbium dihydride YbH₂. Fiz. Tverd. Tela (St. Petersburg) 41, 177–182 (February 1999)     

Dilute gas viscosity of n-alkanes represented by rigid Lennard-Jones chains

ABSTRACT

The shear viscosity in the dilute gas limit has been calculated by means of the classical trajectory method for a gas consisting of chain-like molecules. The molecules were modelled as rigid chains made up of spherical segments that interact through a combination of site–site Lennard-Jones 12-6 potentials. Results are reported for chains consisting of 2, 3, 4, 6, 8, 12 and 16 segments in the reduced temperature range of 0.3–50 for site–site separations of 0.25σ, 0.333σ, 0.40σ, 0.60σ and 0.80σ, where σ is the Lennard-Jones length scaling parameter. The results were used to determine the shear viscosity of n-alkanes in the zero-density limit by representing an n-alkane molecule as a rigid linear chain consisting of n_c ? 1?spherical segments, where n_c?is the number of carbon atoms. We show that for a given n-alkane molecule, the scaling parameters ? and σ are not unique and not transferable from one molecule to another. The commonly used site–site Lennard-Jones 12-6 potential in combination with a rigid-chain molecular representation can only accurately mimic the viscosity if the scaling parameters are fitted. If the scaling parameters are estimated from the scaling parameters of other n-alkanes, the predicted viscosity values have an unacceptably high uncertainty.     

Boron neutralization and hydrogen diffusion in silicon subjected to low-energy hydrogen implantation

Using the hydrogen neutralization of the boron acceptor, the diffusion of hydrogen is investigated in the temperature range 20 °–160 °C. The hydrogenation is performed by low-energy implantation. We observe a fast initial hydrogen migration, followed by a long-time diffusion phase that is described by an effective diffusion coefficientD _eff=D _{0 eff} exp(–E _a/kT) withD _{0 eff}–cm²s^–1 andE _a=(0.83±0.05) eV. No deeper hydrogen migration is detected for implantation times longer than – 30 min. Our data are explained by the build-up of a large amount of molecular hydrogen beneath the surface, which strongly hinders the transfer of the implanted hydrogen to the bulk. The thermal reactivation kinetics of the neutralized boron show a rapid initial step followed by a longtime thermally activated second order phase, which is limited by the recombination of hydrogen into molecules.     

Lattice parameter and optical-energy gap values for Cd x Zn y Mn z Te alloys

Summary Polycrystalline samples of Cd _x Zn _y Mn _z Te alloys (x+y+z=1) were produced by a melt and anneal technique, by annealing at 800°C for 2 weeks giving good equilibrium conditions. Debye-Scherrer X-ray powder photographs were used to determine values of the lattice parametera and the range of solid solution in the zincblende phase. The range of solid solution determined is in good agreement with the previous values for the pseudobinary systems Cd_1−x Mn _z Te and Zn_1−z Mn _z Te. Room temperature measurements of optical absorption and modulated reflectance were made to give values of the energy gapE ₀ as functions of composition. The variation of the parametersa andE ₀ with composition is fitted to a suitable empirical equation, the accuracy of fitting was better than the average experimental scatter. From the fitted parameters, contours of constanta and of constantE ₀ were drawn. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

DFT study of hydrogen storage in Pd-decorated C60 fullerene

Hydrogen storage reactions on Pd-doped C₆₀ fullerene are investigated by using the state-of-the-art density functional theory calculations. The Pd atom prefers to bind at the bridge site between two hexagonal rings, and can bind up to four hydrogen molecules with average adsorption energies of 0.61, 0.45, 0.32, and 0.21 eV per hydrogen molecule. With no metal clustering, the system gravimetric capacities are expected to be as large as 5.8 wt%. While the desorption activation barriers of the complexes nH₂ + Pd–C₆₀ with n = 1 are outside the department of energy (DOE) domain (?0.2 to ?0.6 eV), the desorption activation barriers of the complexes nH₂ + Pd–C₆₀ with n = 2–4 are inside this domain. While the interaction of 1H₂ with Pd + C₆₀ is irreversible at 459 K, the interaction of 2H₂ with Pd + C₆₀ is reversible at 529 K. The hydrogen storage of the irreversible 1H₂ + Pd–C₆₀ and reversible 2H₂ + Pd–C₆₀ interactions are characterised in terms of densities of states, infrared, Raman, and proton magnetic resonance spectra, electrophilicity, and statistical thermodynamic stability.     

Model of adsorption on graphene

A simple M-shaped model has been proposed for the density of states of the π bands of the graphene. The model has been used to derive the expression for the local density of states on the adsorbed atom and to calculate the corresponding occupation numbers for different model parameters. Additional simplifications have made it possible to represent the band contribution n _b to the total occupation number of the adatom n _a in the analytical form. The contributions of local states n _l to n _a = n _b + n _l have been calculated for different parameters. The charge has been numerically evaluated for the case of adsorption of alkali metal atoms on the graphene. The results obtained have been verified using the model of a surface diatomic molecule calculated by the Harrison bond-orbital method. The verification has demonstrated that the charges calculated in terms of radically different models are in good agreement.     

Structural,energetic, and electronic properties of hydrogenated aluminum arsenide clusters

The chemisorptions of hydrogen on aluminum arsenide clusters are studied with density functional theory (DFT). The on-top site is identified to be the most favorable chemisorptions site for hydrogen. And the Al-top site is the preferred one in the most cases for one hydrogen adsorption in (AlAs) _n (n = 2, 5, 6, 8–15) clusters. Top on the neighboring Al and As atoms ground-state structures are found for two hydrogen adsorption on (AlAs) _n except for (AlAs)₂ cluster. The Al–As bond lengths decrease generally as the size of the cluster increases. And there is a slight increase in the mean Al–As bond lengths after H adsorption on the lowest-energy sites of the most AlAs clusters. In general, the binding energy of H and 2H are both found to decrease with an increase in the cluster size. And the result shows that large binding energies (BE) of a single hydrogen atom on small AlAs clusters and large highest occupied and lowest unoccupied molecular-orbital gaps for (AlAs)H and (AlAs)₃H make these species behaving like magic clusters. Calculations on two hydrogen atoms on (AlAs) _n clusters show large BE for (AlAs) _n H₂ with an odd number of n. The stability of these complexes is further studied from the fragmentation energies. (AlAs)₇H₂ and (AlAs)₉H₂ clusters are again suggested to be the stable clusters. On the other hand both the fragmentation energy and the binding energy for (AlAs)₁₃H are close to the lowest values.     

Photonic dark matter portal and quantum physics

We study a model of dark matter in which the hidden sector interacts with standard model particles via a hidden photonic portal.We investigate the effects of this new interaction on the hydrogen atom,including the Stark,Zeeman and hyperfine effects.Using the accuracy of the measurement of energy,we obtain an upper bound for the coupling constant of the model as f≤10~(-12).We also calculate the contribution from the hidden photonic portal to the anomalous magnetic moment of the muon as α_μ≤ 2.2 × 10~(-23)(for the dark particle mass scale 100MeV),which provides an important probe of physics beyond the standard model.