A new method for approximate estimates of the dispersion interaction between two molecules

A new method to evaluate the dispersion interaction between two weakly interacting closed shell molecules is presented. The method is based on a second-order sum-over-states perturbation method, where the nominator is approximated by products of one electron integrals.     

Ab initio studies of internal rotation barriers and vibrational frequencies of (C2H2)2, (CO2)2, and C2H2-CO2

We have performed large-scaleab initio calculations using second order Møller-Plesset perturbation theory (MP2) on the three van der Waals dimers formed from acetylene and carbon dioxide. Intermolecular geometrical parameters are reliably computed at this level of theory. Calculations of vibrational frequencies of the van der Waals modes, currently unobtainable by experimental means, give important information about the intermolecular potential and predict significant large-amplitude motion. Zero point energy contributions are shown to be vital in assessing the relative stability of conformations which are close in energy. Our studies suggest that the barrier to interconversion tunnelling in (CO₂)₂ is significantly smaller than previously inferred and is approximately the same as in (C₂H₂)₂. The reason for the rigidity of (CO₂)₂ is the difference in monomer centre-of-mass separation between ground state and transition state. We also show that, in addition to the previously observedC _2v form, the collinear form of C₂H₂-CO₂ is a local minimum on its potential energy surface.     

A Floating Gaussian Orbital calculation on argon hydrochloride (Ar · HCl)

The electronic structure, properties and binding of the argon hydrochloride (Ar-HCl) complex are discussed in connexion with simpleab initio Floating Gaussian Orbital calculations on the system.     

Isotopic studies and refined structure for the dimethyl ether–CS2 dimer

Rotational spectra of two additional isotopomers of the 1:1 dimer between dimethyl ether (DME) and carbon disulfide (CS₂) have been measured by Fourier-transform microwave spectroscopy, allowing an inertial fit of the structure of this complex. The isotopic data are consistent with a structure in which the CS₂ is aligned nearly perpendicular to the plane of the heavy atoms in DME, with internal motion of the CS₂ from one side of the DME to the other leading to an inversion splitting, ΔE, of 90.34 MHz. This corresponds to a barrier to the tunneling motion of 69(10) cm⁻¹. Ab initio calculations give two structures that are fairly consistent with the experimental rotational constants. One of these is similar to the experimental structure derived from the moments of inertia of three isotopic species, while in the other the CS₂ is aligned roughly along the lone pair direction of the DME, similar to previously observed hydrogen bonded complexes.     

On the development of an effective model potential to describe water interaction in neutral and ionic clusters

Various effective components of the intermolecular interaction of water containing aggregates are examined and their modeling, in terms of the fundamental physical properties of the involved partners, is discussed. We focus, in particular, on the evolution of these components in going from the simplest neutral rare gas–water aggregates to bulk water and ionic water solutions. The analysis singled out that the model chosen to represent the van der Waals interaction as the composition of the action of three dispersion/induction–attraction centres and found to be appropriate to describe the lighter He–H₂O and Ne–H₂O systems, is not adequate to describe the heavier Ar–H₂O aggregate. It was found, instead, that by increasing the mass of the rare gas, other short range contributions to the interaction come into play. Moreover, it was also found that the water molecule tends to behave as a single centre as the strength of the interaction increases. This led to the development of an effective model potential suitable to describe water clusters in the range going from gaseous to condensed phase. The role of electrostatic contributions is also evaluated. The proposed potential model is tested by comparing molecular beam scattering and neutron diffraction experiments with results of molecular dynamics (MD) calculations.     

Calculation of van der Waals interactions involving lipid vesicles

Van der Waals energies of interaction involving vesicles and lipid layers are calculated for different geometries. Results from exact and approximate calculations are compared with some existing experimental data. It is shown that sufficient accuracy can be obtained using relatively simple ‘additivity’ approximations for the contribution of dispersion interactions. A set of calculated results is presented for a small unilamellar vesicle interacting with coated and uncoated metal and polymer surfaces. A lipid coating lowers magnitude of the interaction energy approximately two-fold. The procedure gives a simple possibility to estimate Hamaker constants (and ‘Hamaker functions’) from handbook data taking into account the existing uncertainity in the materials constants of the interacting substances.     

Equilibrium structure of the carbon dioxide-water complex in the gas phase: an ab initio and density functional study

High-level ab initio (MP2/6-311++G(2d,2p) geometry, Gaussian-2, MP4(SDTQ) and QCISD(T) binding energies) and density-functional (Becke3LYP/6-311++G(2df,2pd)) calculations have been performed on the charge-transfer complex between water and carbon dioxide. The complex appears to have two equivalent non-planar minima of C_s symmetry. Minima are separated by transition states with C₁ symmetry, whereas the totally planar structure with C_2v symmetry is a second-order transition state. All the critical points lie at approximately the same energy (less than 0.05 Kj mol⁻¹ difference). Therefore, the experimentally observable structure should be planar. The best equilibrium intermolecular distance for this complex calculated at the MP2/6-311++G(2d,2p) level is 2.800 Å. Our best estimate of the observable intermolecular distance (corrected for anharmonicity) is 2.84 Å, in agreement with the experimentally derived value of 2.836 Å. Our best estimate of the binding energy at the QCISD(T) level, taking into account the variation of the distance owing to anharmonicity and the use of more sophisticated theoretical treatments, is −12.0 ± 0.2 kJ mol⁻¹. Our best estimate of the barrier to internal rotation, also at the MP2/6-311++G(2d,2p) level, is 4.0 kJ mol⁻¹, outside the error limits of the experimental determination (3.64 ± 0.04 kJ mol⁻¹). Density functional theory at the level employed here gives an equilibrium intermolecular distance that is too large (2.857 Å), a binding energy that is too small (8.1 kJ mol⁻¹), attributable neither to geometry nor to the basis set, and also a barrier to internal rotation that is slightly too small (3.39 kJ mol⁻¹). The overall picture is, however, reasonably good.     

Fine Structure of Meniscus of a Wetting Liquid

Equilibrium of a capillary meniscus near a wetting film on a solid in a gravitational field is considered. Unlike previous studies, the present study proves that the fine meniscus structure in a gravitational field is a universal feature—it takes place in a wide variety of problems. In the general case, the capillary meniscus is at a certain distance from the wetting film and does not intersect it. The relation for the minimum distance from the arbitrary meniscus to the solid generalizes the Derjaguin formula for a flat slit. An equation that optimally approximates the meniscus with due account of the contribution of the meniscus/film transition region is derived. A refined solution to the problem of a meniscus on a vertical plate is derived within the perturbation theory. Both gravity and nonuniformity of the vertical static film above a capillary–gravitational meniscus do not affect the minimum distance (the influence is less than 0.0001). A general method for solving sophisticated problems of capillary equilibrium in gravitational field is proposed.     

取代芳烃水中溶解度的测定与估算

本文应用线性溶剂化能相关法回归分析了多种有机有机物的溶解度与范德华体积、Ｌｅｗｉｓ酸性及Ｌｅｗｉｓ碱性之间的相关性，结果表明，溶解度与范德华体积、Ｌｅｗｉｓ酸性及碱性之间呈良好的相关性，用这种方法估算的溶解度值与测定吻合得较好。     

Dye Probes of Nanoclusters in Liquids

Calculations have been carried out to optimize the structure of Van der Waals complexes of methanol with N-methyl-2-nitroaniline, a dye capable of shifts in visible and ultraviolet spectra that depend on (1) solvent dielectric, (2) solvent shell structure, and (3) hydrogen bonding to a slight extent. Hartree–Fock–Roothaan calculations with various basis sets and single-excitation configuration interaction (SCI) are compared to Density–Functional–Theory Time-Dependent Hartree–Fock (DFT-TD) results for three low-energy ultraviolet electronic transitions. Energy-minimized structures are reported for a trimeric complex of two methanol-one water as found using a 6-311G** basis indicating two possible hydrogen-bonding schemes. The effect of a dielectric medium on the ultraviolet spectrum is compared to gas-phase clusters. Electronic transitions are also given for the dye-probe complexed with four or five methanol molecules finding good agreement with observed shifts in the ultraviolet spectrum as found with the TDHF-DFT formalism for the lowest energy transition near 425nm.     

Analytical potential energy function for the Van der Waals molecule He2Ne

A potential energy function has been derived for the two linear isomer structures He₂Ne⁺(X²Σ⁺) using ab initio calculations with the QCISD(T)/6–31++G(d,p) method. Because we use the reasonable dissociation limit (3) instead of the unacceptable one (1), our potential energy function represents considerable topographical features in detail, including the linear [He---Ne⁺---He] structure (R_HeNe = 1.4694 Å, R_He'Ne = 2.0069 Å HeNeHe = 180°) with two symmetric linear saddles (R_HeNe = R_He'Ne = 1.80 Å, HeNeHe = 180° and R_HeNe = 1.5 Å, R_He'Ne = 3.2 A°, HeNeHe = 180°), and the topographical minimum of the [He---He---Ne⁺] structure (R_HeHe = 2.2217 Å, R_HeNe = 1.4426 Å, HeHeNe = 180°), with a linear saddle (R_HeHe' = 3.0 Å, R_HeNe = 1.8 Å, HeHeNe = 180°).     

Theoretical Study on the Rotational Spectra of Ar-D232S Complex

We report a theoretical study on the rotational spectra of Ar-D232S. The intermolecular po- tential energy surface was transformed from our latest ab initio three-dimensional potential of Ar-H232S. The rotational energy levels and wavefunctions of the complex were calcu- lated by using the radial discrete variable representation/angular finite basis representation method and the Lanczos algorithm. The calculated rotational transition frequencies and structural parameters were found to be in good agreement with the available experimental values.     

微制造技术与仿生壁虎腿

壁虎甚至在真空中都可以在垂直光滑的玻璃墙壁上纹丝不动和爬行,显然,这不可能是摩擦力和真空吸力所致,它不分泌任何液体,也不可能是通常的粘合剂作用。对壁虎脚足刚毛吸力的精确测定表明,壁虎腿与物体表面的吸力完全是范德华力相互作用。本文详细介绍了有关壁虎腿仿生研究的最新进展和可能的制备壁虎胶带的微制造方法。     

Nanoscale structure intercrystalline interactions in fat crystal networks

The functional attributes of fat-structured food products such as butter, margarine, chocolate, and ice cream are strongly influenced by the structure and physical properties of an underlying fat crystal network present in the material. Fat crystal networks are arranged in a hierarchical manner with characteristic and quantifiable nano and mesoscale structures. Recent studies carried out by our group have demonstrated that the formation of such a fat crystal network starts with the association of nanoplatelets at the lowest constitutional level. These nanoplatelets interact and aggregate via van der Waals's forces into larger fractal structures, which eventually form a 3-dimensional network responsible for the solid-like characteristics of the material. The purpose of this review is to summarize recent efforts in the characterization and quantification of these recently discovered crystalline nanoplatelets and to discuss the role of van der Waals interactions between them. In addition a brief discussion of previous fractal model will be presented. The new experimental findings on the nanostructural level will then be used to validate our fractal structural–mechanical model of fats (Marangoni, 2000). These new insights will contribute to our knowledge of the nature of fat crystal network in plastic fats at different length scales and the relationship of these structural characteristics to the function and properties of fats.     

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.     

Counterpoise correction is not useful for short and Van der Waals distances but may be useful at long range

This article investigates the errors in supermolecule calculations for the helium dimer. In a full CI calculation, there are two errors. One is the basis set superposition error (BSSE), the other is the basis set convergence error (BSCE). Both of the errors arise from the incompleteness of the basis set. These two errors make opposite contributions to the interaction energies. The BSCE is by far the largest error in the short range and larger than (but much closer to) BSSE around the Van der Waals minimum. Only at the long range, the BSSE becomes the larger error. The BSCE and BSSE largely cancel each other over the Van der Waals well. Accordingly, it may be recommended to not include the BSSE for the calculation of the potential energy curve from short distance till well beyond the Van der Waals minimum, but it may be recommended to include the BSSE correction if an accurate tail behavior is required. Only if the calculation has used a very large basis set, one can refrain from including the counterpoise correction in the full potential range. These results are based on full CI calculations with the aug-cc-pVXZ (X = D, T, Q, 5) basis sets.     

Pseudopotential study of the ground and excited states of Yb2

The ground state of the van der Waals-type lanthanide dimer Yb₂ has been studied by means of relativistic energy-consistent ab initio pseudopotentials using three different core definitions. Electron correlation was treated by coupled-cluster theory, whereby core-valence correlation effects have been accounted for either explicitly by correlating the energetically highest coreorbitals or implicitly by means of an effective core-polarization potential. Results for the first and second atomic ionization potentials, the atomic dipole polarizability, and the spectroscopic constants of the molecular ground state are reported. Low-lying excited states have been investigated with spin-orbit configuration interaction calculations. It is also demonstrated for the whole lanthanide series that correlation effects due to the atomic-like, possibly open 4f-shell in lanthanides can be modeled effectively by adding a core-polarization potential to pseudopotentials attributing the 4f-shell to the core. Received: 3 April 1998 / Accepted: 27 July 1998 / Published online: 9 October 1998