Theory Of Intermolecular Forces Research Articles

Editorial

Editorial

Amyand David Buckingham. 28 January 1930—4 February 2021

David Buckingham was a chemical physicist and theoretical chemist who made fundamental contributions to the understanding of optical, electric and magnetic properties of molecules. Born in Australia, he was an undergraduate at the University of Sydney and the first PhD research student of John Pople (FRS 1961) at Cambridge, and there he made significant advances in the theory of intermolecular forces and nonlinear optics. He then moved to Oxford, where he and his group performed the first direct measurement of a molecular electric quadrupole moment. He was elected to the first chair of theoretical chemistry at the University of Bristol, where he wrote a particularly influential article on molecular moments, higher-order polarizabilities and intermolecular forces. His next appointment was at the University of Cambridge as the first holder of the 1968 Chair of Chemistry, and he was head of a distinguished department of theoretical chemistry for 28 years. With colleagues he pioneered experiment and theory on vibrational optical activity and developed a powerful model to predict the structures of weakly-bound molecules. A man of broad interests and achievements, he played first class cricket in the 1950s.

Improvement of Malang Tahu Quality Using Sweet Potato Natural Dyes by Adsorption Technology

Tahu is a popular culinary product in Malang town. This product is produced from soyabean and rich of protein. Besides, tahu is also rich of water, so that surface of tahu tends to polar. Colorization of tahu by extract of yellow and sweet potatoes is interesting because both sweet potatoes contains different polarity molecular dyes, i.e. polar anthocyanin in the purple sweet potato but non-polar beta carotene in the yellow sweet potato. In this paper, changing of tahu’s color after colorization by extract of both sweet potatoes was observed at different times of adsorption process (2, 4, 6 h), different compositions of the sweet potato and water (100g/1L and 300g/1L), and effect of palm oil addition (250 mL oil/1L water). Result of observation showed that the higher time of adsorption process, the higher ratio of the sweet potato weight and water volume, the darker color of the colorized tahu. Addition of the palm oil just improved extraction of β - carotene from the yellow sweet potato but did not improve the adsorption of the dyes on the tahu surface. Results of this study are used for supporting program of community service DPP SPP 2020 of Inorganic lecturers, as application of adsorption technology using tahu food as adsorbent and application of intermolecular force theory as part of Inorganic Chemistry I course.

John Norman Murrell. 2 March 1932 — 25 January 2016

John Murrell was a theoretical chemist who made important contributions to the understanding of the spectra of organic molecules, to the theory of intermolecular forces and to the construction of potential energy surfaces. He established the University of Sussex as a major centre for research and teaching in theoretical chemistry. He was also a successful writer of textbooks for undergraduate and graduate students on chemical bonding and related topics.

Symmetry‐adapted perturbation theory of intermolecular forces

AbstractBasic concepts and most recent developments of symmetry‐adapted perturbation theory (SAPT) are described. In particular, the methods that combine SAPT with density‐functional theory are discussed. It is explained how SAPT allows one to predict and understand the structure and properties of clusters and condensed phase. The broadest range of such predictions can be achieved by constructing potential energy surfaces from a set of SAPT interaction energies and using these surfaces in nuclear dynamics calculations. © 2011 John Wiley & Sons, Ltd.This article is categorized under:Electronic Structure Theory > Ab Initio Electronic Structure Methods

Characterization of Mixtures. Part 2: QSPR Models for Prediction of Excess Molar Volume and Liquid Density Using Neural Networks.

In our earlier work, we have demonstrated that it is possible to characterize binary mixtures using single component descriptors by applying various mixing rules. We also showed that these methods were successful in building predictive QSPR models to study various mixture properties of interest. Here in, we developed a QSPR model of an excess thermodynamic property of binary mixtures i.e. excess molar volume (V(E) ). In the present study, we use a set of mixture descriptors which we earlier designed to specifically account for intermolecular interactions between the components of a mixture and applied successfully to the prediction of infinite-dilution activity coefficients using neural networks (part 1 of this series). We obtain a significant QSPR model for the prediction of excess molar volume (V(E) ) using consensus neural networks and five mixture descriptors. We find that hydrogen bond and thermodynamic descriptors are the most important in determining excess molar volume (V(E) ), which is in line with the theory of intermolecular forces governing excess mixture properties. The results also suggest that the mixture descriptors utilized herein may be sufficient to model a wide variety of properties of binary and possibly even more complex mixtures.

Modelling organic crystal structures using distributed multipole and polarizability-based model intermolecular potentials

Crystal structure prediction for organic molecules requires both the fast assessment of thousands to millions of crystal structures and the greatest possible accuracy in their relative energies. We describe a crystal lattice simulation program, DMACRYS, emphasizing the features that make it suitable for use in crystal structure prediction for pharmaceutical molecules using accurate anisotropic atom-atom model intermolecular potentials based on the theory of intermolecular forces. DMACRYS can optimize the lattice energy of a crystal, calculate the second derivative properties, and reduce the symmetry of the spacegroup to move away from a transition state. The calculated terahertz frequency k = 0 rigid-body lattice modes and elastic tensor can be used to estimate free energies. The program uses a distributed multipole electrostatic model (Q, t = 00,...,44s) for the electrostatic fields, and can use anisotropic atom-atom repulsion models, damped isotropic dispersion up to R(-10), as well as a range of empirically fitted isotropic exp-6 atom-atom models with different definitions of atomic types. A new feature is that an accurate model for the induction energy contribution to the lattice energy has been implemented that uses atomic anisotropic dipole polarizability models (alpha, t = (10,10)...(11c,11s)) to evaluate the changes in the molecular charge density induced by the electrostatic field within the crystal. It is demonstrated, using the four polymorphs of the pharmaceutical carbamazepine C(15)H(12)N(2)O, that whilst reproducing crystal structures is relatively easy, calculating the polymorphic energy differences to the accuracy of a few kJ mol(-1) required for applications is very demanding of assumptions made in the modelling. Thus DMACRYS enables the comparison of both known and hypothetical crystal structures as an aid to the development of pharmaceuticals and other speciality organic materials, and provides a tool to develop the modelling of the intermolecular forces involved in molecular recognition processes.

On the Representation of Molecular Quadrupole Moments in Terms of Atomic Moments

The magnitude and algebraic sign of the molecular quadrupole moments of the homonuclear diatomic molecules N2, O2, F2, P2, S2 and Cl2 are analyzed by expressing them as a sum of the quadrupole moments of the free atoms and an induced molecular quadrupole due to bond formation. This induced molecular quadrupole is further analyzed in terms of in situ atomic dipole and quadrupole moments constructed following the electron partitioning method suggested by Hirshfeld. These in situ moments are interpreted in terms of the sigma and pi character of the chemical bonds and are compared with those predicted by the DMA method of Stone (The Theory of Intermolecular Forces; Clarendon: Oxford, 1996).

Effect of surface free energy of graded NI–P–PTFE coatings on bacterial adhesion

Biofouling has been recognised as a widespread problem in design and operation of processing equipment, including heat exchangers, cooling water systems and food processing equipment. In the research reported in this paper, the effects of surface free energies on bacterial adhesion were investigated using an intermolecular force theory and the optimum surface free energy of a surface, γ Surface LW on which bacterial adhesion force is minimal was obtained. A graded electroless Ni–P–PTFE coating technique was used to produce anti-bacterial coatings. Initial experimental results showed that these coatings reduced bacterial attachment by 82–97%.

An ab initio study of the potential energy surface of NH 3–CO

Fourth-order Møller–Plesset perturbation theory (MP4) and perturbation theory of intermolecular forces were employed to investigate the potential energy surface of the NH 3–CO complex. Most calculations were performed using a relatively large, well-tempered basis set, though for a few selected structures an augmented basis set with bond functions was used. The global minimum of −1489 μ E h was found for a bent hydrogen-bonded configuration at the intermolecular distance of 4.3 Å. The minimum energy area was discovered to be very wide and flat making the complex extremely flexible. A model potential function for the complex was developed.

Ab initio calculations and modeling of three‐body forces in Ar2H2O

AbstractThe nonadditive interactions in the Ar2H2O cluster, in a variety of geometries, are studied using the supermolecular Møller–Plesset (MP) perturbation theory in conjunction with the perturbation theory of intermolecular forces. The three‐body effect is dissected into several components: the Heitler–London exchange, induction, dispersion, and second‐order supermolecular MP perturbation nonadditivity. The latter term is further analyzed within the framework of pseudodimer treatment. The Heitler–London exchange is dissected into the SE (single exchange) and TE (triple exchange) parts. Analytical representations of the nonadditive terms are discussed. For the exchange (SE) and induction, the multicenter expansions work very well. However, in the case of the three‐body dispersion term, the single‐center dipole‐dipole‐dipole plus dipole‐dipole‐quadrupole expression proves to be more suitable. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002

Ab Initio Study of the CH3F···H2O Complex

The CH3F···H2O complex has been studied using both the supermolecule approach through fourth-order Møller−Plesset perturbation theory (MP4) and perturbation theory of intermolecular forces. Nine configurations have been examined, seven of which were found to be attractive. The global minimum occurs when a bent C−F···H−O hydrogen bond is formed with the C···O distance of 6.15 a0 and the water molecule in the same plane as the hydrogen bond. The binding energy for this geometry is equal to 5291 μEh (3.32 kcal/mol) at the MP4 level of theory. When bond functions are included in the basis set, this configuration is further stabilized to 5739 μEh (3.60 kcal/mol). The two configurations where a hydrogen atom of water is closest to the carbon atom of fluoromethane are repulsive at all distances examined due to electrostatic interactions. The increase of the magnitude of the binding energy when the basis set includes bond functions is primarily due to increased attractiveness of dispersion energy. The electrostatic interaction is the most significant energy component for all seven attractive configurations at their radial minima, particularly for configurations where the C−F bond points toward the H2O molecule. The exchange and dispersion energies are, respectively, the second and third most important contributions to the interaction energy for the seven attractive configurations at their radial minima. The MP2 interaction energy is found to approximate the MP4 interaction energy qualitatively, but underestimates the attraction of the seven attractive configurations at their optimal intermolecular separations by 8−82 μEh. A model potential for the CH3F···H2O system has been developed.

Ab initio potential-energy surface for the He(S1)+NO(X2 Π) interaction and bound rovibrational states

Adiabatic potential-energy surfaces for the A′2 and A″2 states of the He(1S)–NO(X 2Π) complex have been calculated at the restricted coupled cluster level of theory including single, double, and noniterated triple excitations [RCCSD(T)]. The potential-energy surface (PES) of the A′ state has three minima: for the T-shaped geometry, barely skewed toward oxygen (R=6.07 a0, Θ=96.7°, and De≈29.2 cm−1), and for two collinear forms. In contrast, PES of the A″ state has two minima, both related to T-shaped forms: (i) A global minimum, with He shifted toward nitrogen (R=6.27 a0, Θ=76.1°, and De≈25.3 cm−1), and a shoulderlike minimum, with He shifted toward oxygen (R=6.34 a0, Θ=117.6°, and De≈24.5 cm−1). The collinear forms of the A″ state correspond to saddle points. The A′ surface lies above the A″ surface, except in the vicinity of perpendicular arrangement. The interaction energies have been analyzed via perturbation theory of intermolecular forces. The shape and location of the minima is determined primarily by the anisotropy of the exchange component, and stronger repulsion of A′ is due to repulsion between the singly occupied anti-bonding π* orbital and He. A variational calculation of the bound rovibrational states supported by the potential suggests that the HeNO complex is bound by about 7 cm−1. The bound levels correlate with NO rotational levels with j=1/2 and j=3/2, and are well described as nearly free-rotor states in which j (NO rotation) and L (end-over-end rotation of R) are nearly good quantum numbers. Excited intermolecular stretching vibrations are not predicted to be bound.

ESTIMATION OF TRANSPORT PROPERTIES OF LIQUIDS

Based on the theory of intermolecular forces and the Hildebrand relation, a generalized equation in terms of refractive index is proposed to estimate viscosity, thermal conductivity and diffusion coefficients of liquid non-polar compounds at various temperatures. Analytical equations are provided to estimate transport properties of n-alkanes in terms of molecular weight. Average deviations for all three properties of various hydrocarbons from C5 to C20 are within 1 % for a large number of data points. The proposed equation also predicts transport properties of some polar compounds with a reasonable degree of accuracy.

An ab initio study of the Ar–HCN complex

The potential energy surfaces for the ground state of the Ar–HCN complex have been calculated at several levels of theory, including the single and double excitation coupled-cluster method with noniterative perturbational treatment of triple excitation CCSD(T). Calculations have been performed using the augmented correlation-consistent polarized triple zeta basis set supplemented with bond functions (aug-cc-pVTZ+bf). The global minimum with a well depth of approximately 141 cm−1 has been found for the linear Ar–H–C–N geometry (Θ=0.0°) with the distance R between the Ar atom and the center of mass of the HCN molecule equal to 8.52a0. In addition, the potential energy surface has been found to contain a long channel that extended from the bent configuration at R=7.39a0 and Θ=59.7° (a well depth of 126 cm−1) toward the T-shaped configuration with R=7.16a0 and Θ=107.5° (a well depth of 121 cm−1). The interaction energies have been analyzed using perturbation theory of intermolecular forces. The location of the global minimum is determined by the anisotropy of the dispersion and induction effects. The ground vibrational state dissociation energy D0 determined by the collocation method has been found to be 105 cm−1. The wave number of the Σ1 bend amounts to 4.2 cm−1, somewhat below the experimental value (5.5 cm−1).

Ab initio study of the van der Waals interaction of NH(X 3Σ−) with Ar(1S)

The potential energy surface for the Ar(1S)+NH(X 3Σ−) interaction is calculated using the supermolecular unrestricted Mo/ller–Plesset (UMP) perturbation theory approach and analyzed via the perturbation theory of intermolecular forces. The global minimum occurs for the approximate T-shaped geometry with Ar skewed toward the H atom at about Θ=67° and R=6.75 a0. Our UMP4 estimate of the well depth of the global minimum is De=100.3 cm−1 and the related ground state dissociation energy obtained by rigid-body diffusion quantum Monte Carlo calculations (RBDQMC) is D0=71.5±0.1 cm−1. These values are expected to be accurate to within a few percent. The potential energy surface also features a wide plateau in the proximity of Ar-N-H collinear geometry, at ca. 7.0 a0. RBDQMC calculations reveal nearly a free rotation of the NH subunit in the complex.

ArC 2H 2: a challenging system for ab initio calculations

The ArHCCH interaction is investigated by the supermolecular Møller-Plesset perturbation theory and coupled-cluster theory in conjunction with the perturbation theory of intermolecular forces. The interaction energy in this cluster is dissected into the fundamental components such as exchange, induction, and dispersion, and the anisotropy of the overall surface is analysed in terms of the angular behaviors of these components. The shape of the PES of ArHCCH is very sensitive to the level of ab initio theory. The coupled-cluster approach which included the single, double, and approximate triple excitations combined with the aug-cc-pvtz basis set supplemented by bond functions was necessary to obtain the best estimates of D e (within ± 5% error) for two minima: the global one for a skew T-configuration (118 cm −1), and a secondary one for the collinear arrangement (115 cm −1). The PES generated at a lower level of calculation was used in diffusion quantum Monte Carlo (DMC) calculations of the ground and first excited bending vibrational state of the cluster. The expectation values of the coordinates and rotational constants are provided for the ground state. DMC calculations are relatively unsensitive to the details of the PES. The nature and decomposition of three-body interactions in the related cluster Ar 2HCCH were also investigated.

Ab initio study of the O2(X 3Σg−)+Ar(1S) van der Waals interaction

A potential energy surface for the Ar(1S)+O2(X 3Σg−) interaction is calculated using the supermolecular unrestricted Mo/ller–Plesset (UMP) perturbation theory and analyzed via the perturbation theory of intermolecular forces. The global minimum occurs for the T-shaped geometry, around 6.7 a0. Our UMP4 estimate of the well depth of the global minimum is De=117 cm−1 and the related ground state dissociation energy obtained by diffusion Monte Carlo calculations is 88 cm−1. These values are expected to be accurate to within a few percent. The potential energy surface also reveals a local minimum for the collinear geometry at ca∼7.6 a0. The well depth for the secondary minimum at the UMP4 level is estimated at De=104 cm−1. The minima are separated by a barrier of 23 cm−1. The global minimum is determined by the minimum in the exchange repulsion in the direction perpendicular to the O–O bond. The secondary, linear minimum is enhanced by a slight flattening of the electron density near the ends of the interoxygen axis.

Self-Consistent-Field Calculation of Pauli Repulsion and Dispersion Contributions to the Solvation Free Energy in the Polarizable Continuum Model

By using the theory of intermolecular forces, two new expressions for Pauli repulsion and dispersion contributions to the solvation free energy are derived. These expressions contain explicitly the solute electron density and, therefore, can be used directly in the SCF calculation of the solute wave function within the polarizable continuum model (PCM). The final expressions are very simple and include also some intrinsic solvent properties which are, for repulsion, the density, the molecular weight, the number of valence electrons, and for dispersion, the refractive index and the ionization potential. This new approach does not depend on any given intermolecular potential and it can be adapted to any choice of basis set. For small-size basis sets, even minimal, the dispersion contribution is obtained in two steps and includes the effect of adding diffuse and polarization functions, not used in the wave function itself. This method has been implemented in our HONDO package, in a version which includes the cavitation contribution, determined by the Pierotti−Claverie method, and the polarization contribution determined by the Miertus−Scrocco−Tomasi method. Some preliminary results on solutes containing C, H, O, and N are presented for solvation in water, n-hexane, and 1-octanol. The quality of these results, given the simplicity of the PCM, is acceptable and of great interest for future developments.

Ab initio study of the He(1S)+CH(X 2Π) interaction

Potential energy surfaces for the 2A′ and 2A″ states of the He(1S)–CH(X 2Π) complex were calculated using supermolecular unrestricted Mo/ller–Plesset perturbation theory and analyzed via the relevant perturbation theory of intermolecular forces. It has been found that the two states are distinctly different. The potential energy surface (PES) of the A″ state has only a single and relatively deep minimum of De≊335 μEh for the T-shaped geometry, at R=5.0 a0 and Θ=100°. The position of this minimum is determined by the exchange repulsion which is substantially reduced at this geometry. The minimum is unusually deep for a complex of He, and it can be viewed as an example of an incipient chemical bond. In contrast, the A′ state’s PES represents a typical van der Waals interaction which is characterized by two similarly deep minima. The shape and location of these minima are determined primarily by the anisotropy of the dispersion component. The first minimum occurs for the collinear He–C–H arrangement, at R≊7.5 a0, and Θ=0°, and is 55 μEh deep. The second minimum has a troughlike form which joins the region between R=7.5 a0, Θ=140° and R=8.0 a0, Θ=180°. The lowest point is approximately 54 μEh deep and occurs at R=7.5 a0 and Θ=140°.