Showing papers on "Intermolecular force published in 1981"

A computer simulation method for the calculation of equilibrium constants for the formation of physical clusters of molecules: Application to small water clusters

Abstract: : We present a molecular dynamics computer simulation method for calculating equilibrium constants for the formation of physical clusters of molecules. The method is based on Hill's formal theory of physical clusters. In the method, a molecular dynamics calculation is used to calculate the average potential energy of a cluster of molecules as a function of temperature, and the equilibrium constants are calculated from the integral of the energy with respect to reciprocal temperature. The method is illustrated by calculations of the equilibrium constants for the formation of clusters of two to five water molecules that interact with each other by an intermolecular potential devised by Watts. The method is compared with other procedures for calculating the thermodynamic properties of clusters. (Author)

Quantum and statistical mechanical studies of liquids. 10. Transferable intermolecular potential functions for water, alcohols, and ethers. Application to liquid water

Abstract: Transferable intermolecular potential functions (TIPS) suitable for use in liquid simulation are reported for water, alcohols, and ethers. Interaction sites are located on oxygens, hydroxyl hydrogens, and the carbons in alkyl groups. Each type of site has Coulomb and Lennard-Jones parameters chosen to yield reasonable structural and energetic results for both gas-phase dimers and pure liquids. A Monte Carlo simulation of liquid water at 25/sup 0/C using the TIP potential compares favorably with experiment or results from Clementi's CI potential except that the OO radial distribution function is calculated to be too flat beyond the first solvent shell. Simulations of liquid methanol and ethanol have also been carried out as described in the accompanying papers. Overall, in view of the simplicity and transferability of the potentials, the initial results are most encouraging for the treatment of fluids with even more complex monomers and for extension to other types of interaction sites.

Polarization energies of organic solids determined by ultraviolet photoelectron spectroscopy

Abstract: The polarization energies of 44 organic solids were determined by ultraviolet photoelectron spectroscopy in the gaseous and solid states. Condensed polycyclic aromatic hydrocarbons with planar molecular structures were found to have a common value, 1.7 eV, independent of their molecular sizes and also their crystal structures. The common value is approximately interpreted by the first-order expression for the polarization energy. A large variation of values in the range 0.9–3.0 eV was obtained for several compounds. Among them, molecules with intricate structures have smaller values and those with large molecular polarizabilities have larger values than the common value. These results indicate that the polarization energy of an organic solid is mainly determined by two factors: the molecular polarizability and the molecular packing in the solid. Intermolecular interactions in the solid, other than the van der Waals force, also contribute to the value.

Monte Carlo studies of the structure of dilute aqueous sclutions of Li+, Na+, K+, F−, and Cl−

Abstract: Monte Carlo–Metropolis statistical thermodynamic computer simulations are reported for dilute aqueous solutions of Li+, Na+, K+, F−, and Cl−. The calculations are carried out on systems consisting of one ion and 215 water molecules at 25 °C and experimental densities. The condensed phase environment is modeled using periodic boundary conditions. The configurational energies are developed under the assumption of pairwise additivity by means of potential functions representative of nonempirical quantum mechanical calculations of the ion–water and water–water energies. The internal energies, radial distribution functions, and related thermodynamic properties are calculated for each system. The structure of the local solution environment around each dissolved ion is analyzed in terms of quasicomponent distribution functions. The results are compared with analogous calculations on a smaller system to estimate the effect of long‐range forces in the ion–water potential function on the calculated results.

Theoretical studies of hydrogen bonding in liquid water and dilute aqueous solutions

Abstract: Monte Carlo computer simulations of liquid water and dilute aqueous solutions are analyzed in terms of the nature and extent of intermolecular hydrogen bonding. A geometric definition of the hydrogen bond is used. Calculations on liquid water at 25 °C, 37 °C, and 50 °C, were carried out based on the quantum mechanical MCY potential of Matsuoka, Clementi, and Yoshimine and at 10 °C based on the empirical ST2 potential. The effect of a dissolved solute on aqueous hydrogen bonding was studied for dilute aqueous solutions of Li+, Na+, K+, F−, Cl−, and CH4. The nature of the hydrogen bonding was characterized with quasicomponent distribution functions defined as a function of the intermolecular coordinates relevant to hydrogen bonding. The extent of the hydrogen bonding is described using a network analysis approach developed by Geiger, Stillinger, and Rahman. The results on the quasicomponent distribution functions show that the average hydrogen bond angle deviates with 10 °–25 ° from a linear form, quite ind...

Lattice Dynamics of Molecular Crystals

Abstract: 1 Lattice Dynamics.- 1.1 Introduction.- 1.2 The Dynamical Equations in Cartesian Coordinates.- 1.3 Dispersion Curves. Acoustic and Optical Modes.- 1.4 Invariance Conditions.- 1.5 Molecular Coordinates.- 1.6 The Dynamical Equations in Molecular Coordinates.- 2 Symmetry.- 2.1 Space Group Symmetry.- 2.2 Irreducible Representations of the Translational Group.- 2.3 Irreducible Representations of the Space Groups.- 2.4 Time Reversal.- 2.5 Symmetry of the Dynamical Matrix.- 2.6 Symmetry Properties of Vibrational States.- 2.7 Selection Rules.- 3 Intermolecular Potentials.- 3.1 The Crystal Potential.- 3.2 The Intramolecular Potential.- 3.3 The Intermolecular Potential.- 3.4 Intermolecular Force Constants.- 3.5 Lattice Sums and Ewald's Method.- 2.6 Calculation of Phonon Frequencies.- 4 Anharmonic Interactions.- 4.1 Introduction.- 4.2 The Crystal Hamiltonian.- 4.3 Quantum Field Treatment of Phonons.- 4.4 The Hamiltonian Renormalization Procedure.- 4.5 The Self-Consistent Phonon Method.- 4.6 The Method of the Green's Functions.- 4.7 Thermal Strain.- 4.8 Anharmonic Calculations.- 5 Two-Phonon Spectra of Molecular Crystals.- 5.1 Introduction.- 5.2 General Considerations.- 5.3 Two-phonon Density of States.- 5.4 Two-phonon Absorption Coefficients.- 6 Infrared and Raman Intensities in Molecular Crystals.- 6.1 Introduction.- 6.2 Historical Survey.- 6.3 Electrostatic Model of Infrared and Raman Intensities of Molecular Crystals.

Model Calculations of Potential Surfaces of van der Waals Complexes Containing Large Aromatic Molecules

Abstract: In this paper we report the results of model calculations of the nuclear potential surfaces of van der Waals complexes consisting of large aromatic molecules and rare-gas (R) atoms. These potentials were constructed as a superposition of pairwise atom-atom potentials, the R-carbon atom pair potentials being taken from heats of adsorption of rare-gas atoms on graphite, while the R-hydrogen atom pair potentials are estimated by using empirical combination rules. The binding energies of the tetracene (T) complexes TRI are 0.7 kcal mol-' for Ne, 1.5 kcal mol-' for Ar, 1.8 kcal mol-' for Kr, and 2.2 kcal mol-' for Xe, while the equilibrium distance between R and the molecular plane of tetracene is 3.0 A for Ne, 3.45 A for Ar, 3.5 A for Kr, and 3.7 A for Xe. Low-frequency, large-amplitude motion of the R atoms parallel to the molecular plane along the long molecular axis is predicted for TR, and TR2 complexes. The potential for TRI along the long molecular axis has a symmetric double-well form, giving rise to a "tunneling-type'' motion of the R atom. For the TR2 complexes, the configuration with two R atoms located on the same side of the aromatic molecule is energetically favored over that with the two R atoms on opposite sides. No chemical isomers are expected to exist for the TRI and TR2 complexes, while for TR,, complexes with n 1 3 the possibility of the existence of two or more nearly isoenergetic isomers is indicated. The applications and implications of these data for the elucidation of some features of excited-state energetics and dynamics of such van der Waals complexes are considered. van der Waals (vdW) molecules'" are weakly bound molecular complexes held together by attractive (eg, dispersive, electrostatic, charge transfer, hydrogen bonding) interactions between closed- shell atoms or molecules. The primary characteristics of vdW molecules'd are their low (10-1000 cm-I) dissociation energies, the large length of the vdW bond, and the retention of many of the individual properties of the molecular constituents within the vdW complex. During the last few years remarkable progress was achieved in the understanding of the many facets of these interesting systems. These advances were initiated by the utili- zation of supersonic free expansion^^.^ to prepare a variety of fascinating vdW molecules, whose structure, energetics, and dy- namics were explored. The elucidation of the structure, the mapping of the potential surface, and the determination of the energetics of vdW molecules pertain to the basic understanding of intermolecular interactions in chemistry. In this context the ground-state properties of a variety of molecules, e.g., (HF)2,7 ArHF: ArHC1,9 ArHBr,l0 KrHCI," XeHC1,I2 ArCIF," ArOC- S," and the benzene dimer3 were investigated. Studies of in- tramolecular dynamics of vdW molecules in vibrationally excited or electronically vibrationally excited states provided central in- formation on reactive vibrational predissocation processes,57 this being relevant for establishing the general features of intramo- lecular vibrational energy flow in weakly coupled molecular systems. Intramolecular dynamical processes in a variety of vdW molecules, e.g., RIz (R = He, Ne, and Ar),'>'' (C12)2,18 (N2O)2,I9 (NH3)r20 and the ethylene dimer2' were recently explored both experimentally'52' and theoretically.6 The understanding of the reactive and nonreactive dynamics in vdW complexes requires detailed information on potential surfaces. The general conceptual framework advanced for the elucidation of the structural and energetic features of all these small and medium-sized vdW complexes mentioned above rests on a microscopic approach, taking advantage of the advanced techniques of molecular spec- tro~copy~~~~-" to probe the molecular equilibrium configuration, the details of nuclear motion, and the binding energies. This general approach may require some gross modifications when the structure, energies, and dynamics of very large vdW complexes will be considered. Recently, there have been experimental st~dies~~-~~ of very large vdW complexes consisting of aromatic molecules, such as anthracene, tetracene, pentacene, and ovalene

Long range transfer of positive charge between dopant molecules in a rigid glassy matrix

Abstract: Pulse radiolysis has been used to observe and measure the kinetics for intermolecular positive charge (hole) transfer from biphenyl+ or pyrene+ ions to TMPD molecules in rigid 2‐chlorobutane glass at 77 K. These hole transfers occur over distances of about 17 A at 10−6 s, increasing to about 34 A at 102 s. The kinetic data are interpreted in terms of current theories which treat electron transfer processes as radiationless transitions. Estimates of the required electron exchange interactions based on the usual electron tunneling models can not explain the fast reactions observed, even when Coulombic effects on the ’’barrier’’ are considered. A superexchange model is proposed which involves interactions propagated by both negative and positive ion states of the solvent. This model adequately interprets the data in terms of a dominant role of the solvent positive ion states, and is also applicable to negative charge transfer in the condensed phase. In samples containing only one solute (biphenyl or pyrene),...

Quantum and statistical mechanical studies of liquids. 11. Transferable intermolecular potential functions. Application to liquid methanol including internal rotation

Abstract: Two transferable intermolecular potential functions for the methanol dimer have been used in Monte Carlo statistical mechanics simulations of liquid methanol at 25/sup 0/C. One function employs the three-site TIP model for a monomer, while the other retains the methyl hydrogens explicitly in a six-site model. The sampling with the latter potential included the internal rotation for the first time in a Monte Carlo calculation. It is found that the liquid's structure does not alter the dihedral angle distribution from the gas-phase result. Both functions show improved agreement with experimental thermodynamic and structural data in comparison to a previous simulation based on a potential function derived from quantum mechanical calculations. The success of the simple TIP model indicates that treating the methyl hydrogens implicitly is reasonable. Winding hydrogen bonded chains dominate the liquid's structure. Most monomers participate in one or two hydrogen bonds which are bent an average of 20/sup 0/.

Energy Decomposition Analysis of Molecular Interactions

Abstract: In the theoretical study of molecular interactions, ab initio molecular orbital calculations have been applied successfully in predicting the binding energy and the geometry of intermolecular complexes.1–3 In what is called the supermolecule method the entire complex is considered as a supermolecule, and the calculated energy difference between the supermolecule and the monomers is the binding energy. In order to facilitate an interpretation of the results, methods have been proposed4–7 to decompose the interaction energy into physically meaningful energy components such as electrostatic, polarization, charge transfer, and exchange energies. Analyses of many molecular complexes along these lines have provided the basis for elucidating the origin or the nature of various molecular interactions such as hydrogen bonds and electron donor-acceptor complexes.

Vibrational predissociation spectra of (HF) n , n = 2-6

Abstract: Using molecular beam techniques and a tunable infraredlaser, the vibrational predissociation spectra for (HF)n, n = 2 to 6, in the 3000 to 4000 cm−1 range are presented. The vibrational bands have been assigned to intramolecular HF stretching modes and combinations of intra‐ and intermolecular modes. The structures of (HF)n, n = 3 to 6, were found to be cyclic, i.e., each HF molecule is both a proton donor and acceptor.

The influence of angular dependent intermolecular forces on vibrational spectra of solution phase molecules

Abstract: The zeroth, first, and second moments of the solution phase infrared, isotropic Raman, and anisotropic Raman bands of a totally symmetric mode are calculated. The existence of a strong orientationally dependent intermolecular potential is shown to lead to concentration dependent peak frequencies and bandwidths, as well as possible deviations from Beer’s law. Assumining a dominant transition dipole–transition dipole interaction, expressions for the explicit concentration dependence of the infrared, isotropic Raman, and anisotropic Raman first moments are derived and applied to the interpretation of the observed Raman spectra of polar molecules in the solution phase.

Microwave rotational spectrum, molecular geometry, and intermolecular interaction potential of the hydrogen‐bonded dimer OC–HCl

Abstract: The microwave rotational spectra of several isotopic species of a weakly‐bound dimer (CO,HCl) have been measured. For each isotopic species, values of the rotational, centrifugal distortion, and chlorine nuclear quadrupole coupling constants were obtained. These constants are consistent with a linear equilibrium geometry with the atom order OC–HCl, thus establishing the presence of a hydrogen bond to the carbon atom of the CO molecule.. The potential binding of the HCl and CO molecules is also discussed.

The role of capillary wave fluctuations in determining the liquid-vapour interface

Abstract: We investigate the role played by capillary-wave like fluctuations in the determination of the equilibrium density profile and the intermolecular correlation functions of various models of a planar liquid-vapour interface in an external gravitational field. We show that the interfacial profile calculated from the van der Waals model, which is the simplest (squaregradient) approximation in a density functional theory of inhomogeneous fluids, is stable against capillary-wave fluctuations and therefore cannot be used to describe the ‘bare’ interface in a capillary wave model. The density-density correlation function of the van der Waals model exhibits long-ranged correlations in the interface. These are of precisely the same form as those predicted by Wertheim and can be associated with capillary-wave like fluctuations of the Gibbs dividing surface. These fluctuations do not lead to a ‘diffuse’ interfacial profile in the limits of infinite interfacial area and zero gravity; the interfacial thickness remains ...

Development of a flexible intra‐ and intermolecular empirical potential function for large molecular systems

Abstract: The development of a flexible intra- and intermolecular empirical potential function is described, which is designed for investigating the geometric structure of large molecular systems. The intramolecular components in the potential consist of harmonic bond stretching and angle bending terms, out-of-plane deformation terms, and torsional terms; intermolecular components include nonbonding, hydrogen bonding, and electrostatic germs. Bond lengths, angles, and torsional angles are predicted to within 2% of experiment, with most cases being within 1%. The suitability of the intermolecular potential was tested by crystal packing calculations; in all cases the results obtained were in excellent agreement with experiment.

Quantum statistical mechanical model for polarizable fluids

Abstract: The quantum statistical mechanics of a polarizable fluid model is considered using a path‐integral approach The quantum mechanical partition function associated with the internal degrees of freedom of each molecule is approximated by a classical partition function of a polymer ring, while the center‐of‐mass motion of each molecule is treated classically The resulting system of particles can be described by an Ornstein–Zernike equation, which we solve analytically in the mean spherical approximation We give the dielectric constant, free energy, and internal energy of our model in both its continuum‐fluid and lattice‐gas versions (In the former we assume hard‐sphere cores; in both versions we take harmonically oscillating dipole moments as characterizing the internal degrees of freedom, with ideal dipole–dipole intermolecular coupling)

Solvation forces in simple dense fluids. II. Effect of chemical potential

Abstract: The grand canonical ensemble Monte Carlo method is used to calculate the distribution of liquid molecules and the solvation force between two parallel solid surfaces separated by a simple liquid. Neither this distribution nor the solvation force are very sensitive to changes in the chemical potential (i.e., bulk density) of the interstitial liquid.

Monte Carlo studies of adsorption in molecular sieves

Abstract: Adsorption isotherms, heats of adsorption and radial distribution functions for hard sphere and Lennard-Jones molecules in MS-13X have been generated by a Monte Carlo simulation of the grand canonical ensemble. A model which takes into consideration both dispersion and electrostatic energies in zeolite cavities was used for the gas-solid potential energy. Heterogeneity of the zeolite cavity and intermolecular forces between adsorbate molecules were found to be equally important in determining the adsorptive properties. A reference system to test models for adsorption in molecular sieves has been developed.

Intermolecular potentials for ammonia based on SCF–MO calculations

Abstract: The results of SCF molecular orbital calculations on the ammonia dimer have been used in part to parameterize a set of atom–atom potentials. When combined with a charge distribution which reproduces the experimental dipole and quadrupole moments of the monomer, and with independent estimates of the dispersion energy, the resulting intermolecular potential yields a fair description of certain properties of the condensed phases of ammonia. Liquid ammonia is predicted to have a weakly associated character.

Dynamic corrections to Van der Waals potentials

Abstract: A discussion is given of the velocity-dependent forces which arise when two Van der Waals coupled systems move slowly relative to each other. Explicit calculations both for the cases of a molecule interacting with a metal and for two metals interacting with each other indicate that these forces are very small and may safely be neglected in analysing the results of dynamic experiments designed to measure the static Van der Waals force. A result due to Teodorovich (1978) for the case of two metal films in parallel motion is shown to be incorrect.

Theory of high‐spin⇄low‐spin transitions in transition metal compounds induced by cooperative molecular distortions and lattice strains

Abstract: In the previous paper [J. Chem. Phys. 70, 4199 (1979)] the high‐spin ⇄ low‐spin transitions were studied by using the model based on the static treatment of intramolecular distortion, in which the discontinuous spin transitions may be induced by the Jahn–Teller effect. In the present paper the intramolecular distortions are treated as dynamical variables and the intermolecular coupling between the intramolecular distortions is taken into account. It is shown that the results for the present treatment are equivalent to those for the previous treatment except that the meanings of the parameters are different between the two treatments. The effect of the coupling between transition metal ions and a lattice strain on the spin transition is also studied. The lattice strain may drive the spin transition accompanying the cooperative intramolecular distortion, even when the intramolecular coupling is not so strong that it can singly induce the spin transition. The discontinuous change of the lattice strain then takes place together with an occurrence of the cooperative intramolecular distortion. When there is no cooperative intramolecular distortion, the lattice strain varies continuously with temperature and the spin state also varies continuously, only that the discontinuous thermal change of the lattice strain may occur in a very narrow range of the coupling strength.

Intermolecular Forces and Their Evaluation by Perturbation Theory

Abstract: I. Introduction.- II. Symmetry: An Excursion through its Formal Apparatus.- 11.1. Constants of Motion and Projectors.- 11.2. A Review of Group Theory Concepts.- 11.3. A Look to the Symmetric Group.- 11.4. Pauli Principle Implications.- 11.5. Induced and Subduced Representations.- III. Symmetry-Adapted Perturbation Theory: A General Approach.- III.1. Eigenvalue Problems and Partitioning Technique.- III.2. Constants of Motion in the Partitioning Technique.- III.3. Connection between Partitioning Technique and Perturbation Theory.- III.4. The Murrell-Shaw, Musher-Amos and Eisenschitz-London, Hirschfelder-Van der Avoird Formalisms.- III.5. Multidimensional Partitioning Technique and Degenerate Perturbation Theory.- III.6. Upper and Lower Bounds in Second-Order Perturbation Theory by Inner Projection Technique.- IV. Why Symmetry-Adapted Perturbation Theories are Needed?.- IV.1. "Polarization Approximation": Some Hints to its Possible Inadequacy for Intermolecular Interactions.- IV.2. Is the "Polarization Approximation" a Convergent Perturbative Procedure?.- IV.3. "Polarization Approximation" and its Inadequacy for Evaluating Intermolecular Interactions: Claverie's Analysis.- V. Symmetry-Adapted Perturbation Theories at Low Orders: From H2+ to the General Case.- V.1. The Interaction H...H+ as a Test for Symmetry-Adapted Perturbation Theories.- V.2. Some Useful Concepts Arising from an Analysis of the Interaction H...,H+.- V.3. A Basic Partition of the Interaction Energy Through the Second-Order for Many-Electron Subsystems.- V.4, Many-Electron Systems: the Problems Posed by Our Ignorance of Exact Unperturbed Eigenstates.- VI. The Calculation of the 1-St Order Interaction Energy.- VI.1. Coulombic Contribution to the 1-st Order Interaction Energy: a Useful Expression in Terms of the Charge Density Matrix.- VI.2. The Evaluation of the Coulombic Energy.- VI.3. Coulombic Interaction Energy in the Approximation of Neglecting Overlap Effects.- VI.4. An Assessment of the Importance of Charge Overlap Effects.- VI.5. The Exchange Contribution to the 1-st Order Interaction Energy: an Approximate Evaluation.- VI.6. Dependence of the First-Order Energy on the Wave-function Quality.- VII. The Second-order Contribution to the Interaction Energy.- VII.1. Second-order Polarization Energy in the Approximation of Neglecting Charge Overlap Effects.- VII.2. Induction and Dispersion Coefficients for Two Interacting Linear Molecules.- VII.3. Induction Energy Coefficients and Static Polarizabilities of Molecules: Two Problems in One.- VII.4. The Evaluation of the Dispersion Energy Coefficients.- VII.5. Determination of Upper and Lower Bounds to Dispersion Energy Coefficients.- VII.6. Nonexpanded Form of the 2-nd Order Polarization Energy.- VII.7. Approximate Evaluation of Exchange Polarization Effects.- VIII. Epilogue.- *Appendix A.- *Appendix B.- *Appendix C.- *Appendix D.- *References.

Far infrared spectra of strongly polar molecules in solid solution. I. Acetonitrile

Abstract: Strongly polar molecules such as acetone, nitromethane, and acetonitrile imbedded in an inert gas matrix give rise to characteristic absorption patterns below 150 cm−1. The bands observed in the case of acetonitrile are due to an activated phonon band, to two vibrations of a monomer molecule within the polarized cage of inert gas atoms, and to two intermolecular vibrations of an antiparallel dimer.

The Role of Surface and Intermolecular Forces in Thin Film Lubrication

Abstract: This paper describes four main types of lubrication. in hydrodynamic lubrication the two main factors are the attachment of the molecules to the wall which determines the boundary conditions of flow: and intermolecular forces which determine the viscosity. Oil film thicknesses are of the order 10 −3 cm. In elastohydrodynamic lubrication (EHL) the high pressures produce a prodigious increase in lubricant viscosity and ultimately the film (usually 10 −5 cm thick) behaves like a solid wax. Although the Eyring theory of liquid viscosity is generally rejected by liquid-state physicists it is remarkably successful in describing the behaviour of lubricant fluids over an enormous range of parameters. Its main features are discussed. In boundary lubrication adsorbed or chemically attached molecular layers of fatty acids and similar substances protect the surface when EHL fails. the film may be only a few tens of angstroms thick and there is evidence that sliding occurs between the ends of the molecular chains. Finally thin films of linear (high density) polyethylene or of PTFE can be spread over surfaces to provide lubricating films or order 10 −6 cm thick. Here sliding occurs between chains orientated along the direction of sliding. The common feature of the three types of lubrication is that the shear strength τ of the film can be expressed in the form where p is the contact pressure and α a constant which lies between 0.05 and 0.1 for a very wide range of materials. An attempt is made to explain this in terms of molecular processes. the simplest approach is employed going back to the ideas of Belidor (1737): this involves a Coulomb type mechanism on a molecular scale. However, the present model does not attempt to solve the problem of intermolecular forces but links the energy dissipated in sliding with the surface energy of the material. the most significant innovation is based on the recognition that in all the cases considered the pressure-activation volume in the sliding process does not depend on the size of the molecules: for a wide range of hydrocarbon materials it lies between 50 and 100 (A) 3 and appears to correspond to a transgauche rotation of a C-C bond or to a “crank-shaft” motion. It is suggested thats liding involves (i) a thermally activated movement of this type providing a favourable orientation for easy slip and (ii) a small tangential stressto overcome the local intermolecular forces. The paper is speculative and should be treated primarily as a ballon d'essai.

A Monte Carlo study of fluid water in contact with structureless walls

Abstract: A canonical ensemble Monte Carlo method has been used to examine the structure of fluid water in the space between two walls, each of which exerted a 9–3 potential. The intermolecular pair potential between the water molecules was that proposed by Rowlinson from the properties of ice and steam. The simulation involved 216 water molecules at a temperature of 298 K and employed periodic boundary conditions in the two directions parallel to the surface. In addition to the usual thermodynamic quantities we have collected singlet distributions for the oxygen and hydrogen atoms and the dipole vector, and pair distributions in three laminar regions between the walls for interatomic and dipole pairs. The thermodynamic and structural properties of our non-uniform sample are compared with those of uniform bulk water from simulation data.

Topological distribution functions and the second virial coefficients of ring polymers

Abstract: A new method (a topological moment method) is presented for treating statistical problems of ring polymer chains of which the topological state (Gauss linking coefficient) is prescribed. It is shown that the topological interaction among ring polymers formally resembles the excluded volume effect among linear polymers. A ’’topological parameter γ’’ which corresponds to the binary cluster integral β in the excluded volume problem is newly introduced for representing the strength of the topological interaction among submolecules. The parameter γ is given as a function of bond length, bond angle, internal‐rotational potential, and of interaction potentials among chain elements. Analytical expressions for the distribution function of the intermolecular distance and the second virial coefficient are derived and they are computed numerically.