Semiclassic approach within the He atom sphere model

The helium atom doubly excited‐states energy levels are calculated for the ¹S‐state. The He atom is considered as the three‐atomic molecule. The electrons are supposed to move on the sphere of the equal radius. The rotation is described by the Euler angles, which can be divided in a standard way. Then, the hyperspherical coordinates are introduced. The adiabatic approach allows us to solve the equation on interelectron angle θ. We used the contour integral method for this equation. The equation on the hyperradius R was solved according to the semiclassic approach. The obtained results are in good agreement with those of some other works. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

On the phase behavior of hard aspherical particles

We use numerical simulations to understand how random deviations from the ideal spherical shape affect the ability of hard particles to form fcc crystalline structures. Using a system of hard spheres as a reference, we determine the fluid-solid coexistence pressures of both shape-polydisperse and monodisperse systems of aspherical hard particles. We find that when particles are sufficiently isotropic, the coexistence pressure can be predicted from a linear relation involving the product of two simple geometric parameters characterizing the asphericity of the particles. Finally, our results allow us to gain direct insight into the crystallizability limits of these systems by rationalizing empirical data obtained for analogous monodisperse systems.     

Chemical potential of a hard sphere fluid adsorbed in model disordered polydisperse matrices

We consider a model for adsorption of a simple fluid in disordered polydisperse adsorbents. The fluid consists of hard sphere particles. On the other hand, the adsorbents of this study are modeled as a collection of hard spheres with their diameter obeying a certain distribution function. Our focus is in the evaluation of the chemical potential of the fluid immersed in such a polydisperse material. It permits us to obtain porosity and pore size distribution for the adsorbent, as well as a set of adsorption isotherms. The latter have been calculated theoretically and by grand canonical Monte Carlo simulations. We observe that the width of assumed polydispersity distribution affects all the properties of the system. Nevertheless, the effect of matrix packing is dominant in determining adsorption for this class of models. We are convinced that the matrix structures generated via more sophisticated algorithms would exhibit stronger effects of polydispersity on the entire set of properties of adsorbed simple fluids.     

Magnetic properties of nitric oxide adsorbed within channel crystals

The crystalline one-dimensional compounds, [M₂(bza)₄(pyz)]_n (bza = benzoate; pyz = pyrazine; M = Cu^II (1)) and [M₂(bza)₄(2-mpyz)]_n (2-mpyz = 2-methylpyrazine; M = Rh^II (2), Cu^II (3)), demonstrate gas absorbency of NO. The amounts of adsorbed NO gas are 0.61 for 1, 0.30 for 2, and 0.23 for 3 per M₂ unit at 195 K (800 Torr). The crystals of 1 adsorbed more NO molecules than did those of 2 and 3. The magnetic susceptibilities of the NO-inclusion crystals indicate that included NO molecules interact antiferromagnetically with neighboring guests without dimerization to N₂O₂. Magnetic behaviors indicated NO aggregation in the narrow 1D channels of 1–3 under unsaturated adsorption conditions.     

Encapsulation of metal particles within the wall structure of mesoporous carbons

A method for the production of mesoporous carbon, with metal particles encapsulated in the walls to prevent leaching, is demonstrated by the synthesis of a cobalt containing CMK1 structure.     

On the Landau bicritical point for hard biaxial particles

We consider the isotropic symmetry breaking bifurcations for an arbitrary free energy functional describing hard non-spherical particles. It is shown that a large class of functionals for hard biaxial particle fluids that incorporate excluded volume effects solely through the distribution averaged pair excluded volume all have Landau bicritical points at the same particle shape parameters.     

Toward a fuzzy atom view within the context of the quantum theory of atoms in molecules: quasi-atoms

The notion of quasi-atoms is introduced within the context of the quantum theory of atoms in molecules. Being a subset of the quantum divided basins that were introduced previously, quasi-atoms are the quantum subsystems that are practically indistinguishable from the topological atoms; thus, revealing the continuous evolution of quantum divided basins into topological atoms. This indistinguishability is rooted in the limited accuracy of chemical observations; they are not sensitive to discriminate a topological atom from its associated quasi-atoms. In this regard, it is disclosed that the set of quantum atoms is in a wide-range including members other than topological atoms; the quasi-atoms are concrete examples. Finally, the idea of the fuzzy set of atoms that is foreign to the disjoint partitioning schemes for which the orthodox QTAIM is a classic example is extended employing the set of quasi-atoms.     

氢原子在金属锂表面台阶附近吸附和表面扩散行为的ab initio研究

取Li7H和Li9H两个原子簇模拟氢原子与含台阶的金属锂表面的相互作用, 以小基组用ab initip方法计算了体系的吸附和表面扩散势能面(或势能曲线)。结果表明: (1)对Li7H体系, 台阶面附近沿垂直边棱方向存在三种不同的桥位吸附位, 最稳定的吸附位在上台面接近台阶边棱处, 台阶面显著地改变了表面扩散活化能, 台阶边棱处有一个较高的势垒。于是, 迁移原子将会在台阶边棱处受到反射, 并可被捕获于台阶面上及其附近。由势能面确定了最低能量表面扩散途径。(2)对Li9H体系, 在Li7H原子簇基础上增加次表面层两个锂原子后, 表面扩散活化能略有减小, 氢原子在上台面的桥位吸附更趋稳定, 各吸附位相对稳定性及势垒内何位置几无改变, 这些结果显示了台阶面对氢原子的化学吸附和表面扩散发生扰动, 台阶边棱对表面扩散起着重要作用。     

Dynamical hydrogen atom tunneling in dichlorotropolone: a combined quantum, semiclassical, and classical study

Based on the Cartesian Reaction Surface framework we construct a four-dimensional potential for the tropolone derivative 3,7-dichlorotropolone, a molecule with an intramolecular O-H...O hydrogen bond. The reduced configuration space involves the in-plane hydrogen atom coordinates, a symmetric O-O vibrational mode, and an antisymmetric mode related to deformations of the seven-membered ring. The system is characterized in terms of quantum mechanical computations of the low-lying eigenstates as well as a classical and semiclassical analysis of spectra obtained via Fourier transforming autocorrelation functions. For the semiclassical analysis we utilize the amplitude-free correlation function method [K. Hotta and K. Takatsuka, J. Phys. A 36, 4785 (2003)]. Our results demonstrate substantial anharmonic couplings leading to highly correlated wave functions even at moderate energies. Furthermore, the importance of dynamical tunneling in tropolone is suggested since many low-lying states--including the ground state--lie above the classical saddle point but nevertheless appear as split pairs.     

YinYang atom: a simple combined ab initio quantum mechanical molecular mechanical model

A simple interface is proposed for combined quantum mechanical (QM) molecular mechanical (MM) calculations for the systems where the QM and MM regions are connected through covalent bonds. Within this model, the atom that connects the two regions, called YinYang atom here, serves as an ordinary MM atom to other MM atoms and as a hydrogen-like atom to other QM atoms. Only one new empirical parameter is introduced to adjust the length of the connecting bond and is calibrated with the molecule propanol. This model is tested with the computation of equilibrium geometries and protonation energies for dozens of molecules. Special attention is paid on the influence of MM point charges on optimized geometry and protonation energy, and it is found that it is important to maintain local charge-neutrality in the MM region in order for the accurate calculation of the protonation and deprotonation energies. Overall the simple YinYang atom model yields comparable results to some other QM/MM models.     

Numerical study of the equilibrium properties of suspended particles surrounded by a permeable membrane with adsorbed charges

The network simulation method is used to calculate the electrostatic potential distribution for suspended spherical particles made of a charged core surrounded by a permeable membrane with adsorbed charges. The structure of the equilibrium diffuse double layers on both sides of the membrane-electrolyte solution interface is analyzed considering an anion adsorption process described by a Langmuir-type isotherm. It is shown that the thickness of the double layer in the membrane strongly depends on the adsorption constant, while it is almost independent of this constant in the electrolyte solution. The evolution of the electric potential on the core as a function of the electrolyte concentration is also analyzed.     

On the hydrogen atom beyond the Born–Oppenheimer approximation

Recently a new formulation of quantum mechanics has been suggested which is based on the concept of signed particles, that is, classical objects provided with a position, a momentum and a sign simultaneously. In this article, we comment on the plausibility of simulating atomic systems beyond the Born–Oppenheimer approximation by means of the signed particle formulation of quantum mechanics. First, to show the new perspective offered by this new formalism, we provide an example studying quantum tunnelling through a simple Gaussian barrier in terms of the signed particle formulation. Then, we perform a direct simulation of the hydrogen atom as a full quantum two‐body system, showing that the formalism can be a very promising tool for first‐principle‐only quantum chemistry.     

An exact formula for the contact value of the density profile of a system of charged hard spheres near a charged wall

An exact formula for the contact value of the density of a system of charged hard spheres near a charged hard wall is obtained by means of a general statistical mechanical argument. In addition, a formula for the contact value of the charge profile in the limit of large field is obtained. Comparison with the corresponding expressions in the Poisson-Boltzmann theory of Gouy and Chapman shows that these latter expressions become exact for large fields, independent of the density of the hard spheres.     

Stripped ion–helium atom collision dynamics within a time-dependent quantum fluid density functional theory

A nonperturbative, time-dependent (TD) quantum mechanical approach is described for studying the collision dynamics between the He atom and a fully stripped ion. The method combines quantum fluid dynamics and density functional theory to solve two coupled equations: one for the trajectory of the projectile nucleus and the other for the electronic charge distribution of the target atom. The computed TD and frequency-dependent properties provide detailed features of the collision process. Inelastic and ionization cross sections are also reported. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67: 251–271, 1998     

Influence of hydrogen bonding on the properties of water molecules adsorbed in zeolite frameworks

Three hydrated aluminosilicate frameworks—LiABW, NaNAT, and BaEDI—are partly optimized with the periodic Hartree–Fock CRYSTAL95 code. In particular, we optimized the positions of the adsorbed water molecules including the positions of the framework cations (ABW, NAT) or part of the framework atomic positions (ABW). This allowed us to compare cation–water clusters in the gas and adsorbed states and discuss the influence of hydrogen bonding to the framework oxygen atoms or to the neighbor water molecules on the atomic properties (quadrupole coupling constant, anisotropy of electric field gradient) of the adsorbed water molecules. The LiBIK structure obtained from X‐ray diffraction is also considered to illustrate the hydrogen bonds occurring between adsorbed water molecules. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

氟原子与氢分子共线反应几率的量子散射计算

基于最新的6SEC势能面,用邓从豪等提出的LCAC-SW方法计算得到了共线反应F+H~2(v=0)→HF(v')+H的态-态反应几率,计算结果准确地反映出势能面的特点,进一步证明LCAC-SW方法是一成功的量子散射方法。     

On similitude of near wall turbulence in viscous sublayer

Power spectral density (PSD) of wall velocity gradient fluctuations has been measured using electrochemical (electrodiffusion) method in two rectangular channels with different hydraulic diameters and aspect ratio. The problem of the probes inertia at high frequency range has been smoothed by means of the transfer function; the reliability of the obtained results is justified by using of two circular probes with different diameter. For studied range of Reynolds numbers (6 × 10³ < Re _h < 4 × 10⁴) all spectra functions tend to a unique curve when a suitable dimensionless coordinates are used. These coordinates depend on the mean value of the velocity gradient S, the intensity of the velocity gradient fluctuations [`(s￠² )]overline {s'^2 } and the liquid viscosity ν, only. Thus, the obtained results reveal the similitude of the turbulence in the viscous sublayer with respect to Re number and flow geometry. Sure, this hypothesis should be tested with more representative base of experimental data. The revealed similitude can be important for chemical engineering applications. Indeed, for these applications the Reynolds numbers are rather small and correspond to the studied range and the intensity of the velocity gradient fluctuations are well related with the mean value of the velocity gradient value. So, the knowing of the mean velocity gradient S allows the prediction of the PSD of the velocity gradient fluctuations, if the viscosity of the fluid ν is known.     

On the determination of the structure and tension of the interface between a fluid and a curved hard wall

The structure and tension of the interface between a fluid and a spherically shaped hard wall are studied theoretically. The authors show the equivalence of different expressions for the surface tension and Tolman length using the squared-gradient model and density functional theory with a nonlocal, integral expression for the interaction between molecules. Even though both these models yield equilibrium density profiles that do not satisfy the wall theorem, they still obey the basic requirement of mechanical equilibrium. The authors trace back the origin of the difference between these two observations to the (lack of) continuity of the cavity function at the hard wall.