Van der Waals volume fragmental constants

Van der Waals (vdW) volumes (V_w,x) of 117 molecular fragments (X) have been calculated by numerical integration of the van der Waals envelope using the hard-sphere approximation, standard geometries, and effective atomic van der Waals radii which were determined by comparison of their effects on the predicted sterically allowed conformations of peptides with observed crystal structures. vdW volume fragmental constants give accurate estimates of molecular, vdW volume as sum of approximate V_w,xs.     

Ion attachment to Van der Waals clusters

Mixed ionized clusters have been produced in a supersonic nozzle beam experiment by attachment of stagnant cations (i.e. NO⁺ and Xe⁺) to neutral van der Waals clusters (i.e.Ar _n ) within a Nier type ion source. This new ionization technique leads to less fragmentation than electron impact ionization and the measured cluster distributions exhibit icosahedral shell and subshell closures which have not been detected in the case of electron impact of Ar _n -clusters ionization so far. Additionally, the obtained appearance energies and metastable fractions give insight into the production mechanism and the stability of the resulting ions.     

Van der Waals Effects on semiconductor clusters

Van der Waals (vdW) interactions play an important role on semiconductors in nanoscale. Here, we utilized first‐principles calculations based on density functional theory to demonstrate the growth mode transition from prolate to multiunit configurations for Ge_n (n = 10–50) clusters. In agreement with the injected ion drift tube techniques that “clusters with n < 70 can be thought of as loosely bound assemblies of small strongly bound fragments (such as Ge₇ and Ge₁₀),” we found these stable fragments are connected by Ge₆, Ge₉, or Ge₁₀ unit (from bulk diamond), via strong covalent bonds. Our calculated cations usually fragment to Ge₇ and Ge₁₀ clusters, in accordance with the experiment results that the spectra Ge₇ and Ge₁₀ correspond to the mass abundance spectra. By controlling a germanium cluster with vdW interactions parameters in the program or not, we found that the vdW effects strengthen the covalent bond from different units more strikingly than that in a single unit. With more bonds between units than the threadlike structures, the multiunit structures have larger vdW energies, explaining why the isolated nanowires are harder to produce. © 2015 Wiley Periodicals, Inc.     

Van der Waals Attraction between Spherical Particles

A new and single correction function which could be used with the London equation to account for the retardation effect on van der Waals attraction, was recently proposed. The function is simple enough to permit closed-form solutions to be obtained by the Hamaker–De Boer approach for macrobodies of a few different shapes. In this paper, closed-form solutions are presented for sphere–half space and sphere–sphere systems. The results are shown to agree well with those which employ Overbeek correction functions.     

Average and extreme multi-atom Van der Waals interactions: Strong coupling of multi-atom Van der Waals interactions with covalent bonding

Background  

The prediction of ligand binding or protein structure requires very accurate force field potentials – even small errors in force field potentials can make a 'wrong' structure (from the billions possible) more stable than the single, 'correct' one. However, despite huge efforts to optimize them, currently-used all-atom force fields are still not able, in a vast majority of cases, even to keep a protein molecule in its native conformation in the course of molecular dynamics simulations or to bring an approximate, homology-based model of protein structure closer to its native conformation.     

Van der Waals surface graphs and molecular shape

A van der Waals surface graph is the graph defined on a van der Waals surface by the intersections of the atomic van der Waals spheres. A van der Waals shape graph has a vertex for each atom with a visible face on the van der Waals surface, and edges between vertices representing atoms with adjacent faces on the van der Waals surface. These are discrete invariants of three‐dimensional molecular shape. Some basic properties of van der Waals surface graphs are studied, including their relationship with the Voronoi diagram of the atom centres, and a class of molecular embeddings is identified for which the dual of the van der Waals surface graph coincides with the van der Waals shape graph. This revised version was published online in July 2006 with corrections to the Cover Date.     

聚合物流体的范德华凝聚行为

研究了由聚合物的范德华作用导致的凝聚行为. 研究发现, 尽管聚合物同小分子的相行为的形成原因不同(聚合物体系的相行为是由动能、构象熵项和范德华作用能三项相互竞争的结果, 而小分子的相行为是由动能和范德华作用能相互竞争的结果), 但是它们表现出了极为相似的相行为.     

Van der Waals dispersion forces between dielectric nanoclusters

Various methods are evaluated for their ability to calculate accurate van der Waals (VDW) dispersion forces between nanoclusters. We compare results for spheres using several methods: the simple Hamaker two-body method, the Lifshitz (DLP) theory with the Derjaguin approximation, the Langbein result for spheres, and our "coupled dipole method" (CDM). The assumptions and shortcomings of each method are discussed. The CDM accounts for all n-body forces, does not assume a continuous and homogeneous dielectric function in each material, accounts for the discreteness of atoms in the particles, can be used for particles of arbitrary shape, and can exactly include the effects of various media. At present, the CDM does not account for retardation. It is shown that even for spheres, methods other than the CDM often give errors of 20% or more for VDW dispersion forces between typical dielectric materials. A related calculation for metals reveals an error in the Hamaker two-body result of nearly a factor of 2.     

利用全范德华力作用原理制备仿生干型高分子粘合材料--"壁虎胶带"

壁虎脚足与物体表面是完全的范德华力。介绍一种全新的模仿壁虎脚足刚毛、利用全范德华力作用原理制造的干型高分子粘合材料——“壁虎胶带”及其粘合原理。     

Van der Waals supercritical fluid: exact formulas for special lines

In the framework of the van der Waals model, analytical expressions for the locus of extrema (ridges) for heat capacity, thermal expansion coefficient, compressibility, density fluctuation, and sound velocity in the supercritical region have been obtained. It was found that the ridges for different thermodynamic values virtually merge into single Widom line only at T < 1.07T(c), P < 1.25P(c) and become smeared at T < 2T(c), P < 5P(c), where T(c) and P(c) are the critical temperature and pressure. The behavior of the Batschinski lines and the pseudo-Gruneisen parameter γ of a van der Waals fluid were analyzed. In the critical point, the van der Waals fluid has γ = 8/3, corresponding to a soft sphere particle system with exponent n = 14.     

Van der Waals complexes of perylene with rare-gas atoms

Fluorescence excitation spectra of weakly bound complexes between perylene (P) and rare-gas atoms (R) have been observed. Model calculations of potential surfaces of vdW complexes consisting of perylene and rare-gas atoms show that geometrical re-organisation is important and that thermal population of intermolecular P-R vibrational states may account in part for unresolved broadening at moderate stagnation pressures.     

Van der Waals radii of metals from spectroscopic data

The lack of information about the van der Waals radii of metals can be compensated for by using the results of spectroscopic investigations of van der Waals molecules. It has been shown that the interatomic distances in these molecules obey an additive scheme if one allows for the polarization effects. The van der Waals radii of the alkali metals, Ag, Mg, Zn, Cd, Hg, B, Al, In, and Si, have been determined from the interatomic distances in their heteroatomic molecules with atoms of noble gases. Use of the obtained radii for crystal chemistry is discussed.Translated fromIzyestiya Akademil Nauk. Seriya Khimicheskaya, No. 8, pp. 1374–1378, August, 1994.     

Van der Waals interactions between surfaces of biological interest

Microscopic and macroscopic approaches to calculations of long-range Van der Waals interactions between bodies are reviewed. Expressions are presented for various geometries, including planar-layered structures, sheathed spheres and rods. Retardation effects are shown to reduce dispersion interactions in a similar fashion in both approaches. Pair summation procedure gives 10–25% greater values of dispersion interactions than the macroscopic approach. Orientation effects, previously neglected in microscopic approaches are strongly dependent on many-body effects. When orientation effects are included in a pair summation procedure, its calculated values are close to those calculated with the macroscopic approach.Experimentally determined force values are in agreement with calculated ones for distances of separation above 15 Å in vacuum. In general, the theory is insufficient for yielding forces at distances of separation below 20 Å in water.Determination of Van der Waals parameters from refractive indices of pure liquids and solutions is described. Within 5%, dispersion coefficients are independent of concentration of solution, and isotropic electronic polarizabilities agree with those obtained by the addition of bond polarizabilities. Van der Waals parameters of several major components of cellular surfaces and intercellular media are arranged according to an ascending sequence: water<alkanes<phospholipids<proteins and cholesterol<sugars.Variations in compositions, distances of separation, and layer thicknesses are considered in the calculation of the interactions between cellular surfaces, both in planar and spherical systems, including phospholipid vesicles. In planar-cellular systems, Hamaker coefficients vary between 4 x 10^-15 and 6 x 10^-14 erg; at 50 Å distance of separation the free energies and forces are 210 to 1600 kT/μm², and 4 x 10^-5 to 3 x 10^-4 dynes/μm² respectively. The total potential curve, including electrostatic interactions, is calculated and the questions of cellular adhesion and fusion of phospholipid vesicles are discussed.     

Van der Waals Onteractions in molecular complexes of tetracyanoethylene

The interaction energy of complexes formed between methylbenzenes and tetracyanoethylene is calculated by two procedures. The first one is the monopoles-bond polarizabilities procedure previously described, while the second is derived from the semi-empirical treatment proposed by Kitaygorodsky. A satisfactory agreement is obtained between the calculated energies and the observed energies of formation in the gas phase. The dipole moment induced by mutual electronic polarization of the components is calculated for the Durene-Tetracyanoethylene complex, and is found to account for the major part of the observed dipole.

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Zusammenfassung Die Wechselwirkungsenergie von Komplexen, die aus Methylbenzenen und Tetracyanäthylen gebildet werden, wird mit Hilfe von zwei Verfahren berechnet. Das erste ist das Verfahren der Monopol-Bindungs Polarisierbarkeiten, welches bereits beschrieben wurde. Das zweite Verfahren wird aus der halbempirischen Methode, die durch Kitaygorodsky vorgeschlagen wurde, hergeleitet. Eine befriedigende Übereinstimmung zwischen den berechneten und beobachteten Formationsenergien in der Gasphase wird erzielt. Das Dipolmoment, welches durch die gegenseitige elektrische Polarisation der Komponenten induziert wird, wird für den Durol-Tetracynäthylen-Komplex ausgerechnet. Es stimmt im wesentlichen Teil mit dem beobachteten Dipolmoment überein.

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Résumé L'énergie d'interaction des complexes formés entre les methylbenzenes et le tetracyanoéthylene est évaluée au moyen de deux procédés: le premier est le procédé dit «monopoles-polarisabilités de liaison» tandis que le second est dérivé du traitement semi-empirique proposé par Kitaygorodsky. Un accord satisfaisant est obtenu entre les valeurs calculées et les énergies expérimentales de formation en phase gazeuse. Le dipole induit par polarisation électronique mutuelle des constituants est calculé dans le cas du complexe durene-tetracyano éthylène et rend compte de la majeure partie du dipole observé.