M. P. Tosi

Interaction of atoms and molecules with solid surfaces

There is considerable interest, both fundamental and technological, in the way atoms and molecules interact with solid surfaces. Thus the description of heterogeneous catalysis and other surface reactions requires a detailed understand ing of molecule-surface interactions. The primary aim of this volume is to provide fairly broad coverage of atoms and molecules in interaction with a variety of solid surfaces at a level suitable for graduate students and research workers in condensed matter physics, chemical physics, and materials science. The book is intended for experimental workers with interests in basic theory and concepts and had its origins in a Spring College held at the International Centre for Theoretical Physics, Miramare, Trieste. Valuable background reading can be found in the graduate-Ievel introduction to the physics of solid surfaces by ZangwilI(1) and in the earlier works by Garcia Moliner and F1ores(2) and Somorjai.(3) For specifically molecule-surface interac tions, additional background can be found in Rhodin and Ertl(4) and March.(S) V. Bortolani N. H. March M. P. Tosi References 1. A. Zangwill, Physics at Surfaces, Cambridge University Press, Cambridge (1988). 2. F. Garcia-Moliner and F. Flores, Introduction to the Theory of Solid Surfaces, Cambridge University Press, Cambridge (1979). 3. G. A. Somorjai, Chemistry in Two Dimensions: Surfaces, Cornell University Press, Ithaca, New York (1981). 4. T. N. Rhodin and G. Erd, The Nature of the Surface Chemical Bond, North-Holland, Amsterdam (1979). 5. N. H. March, Chemical Bonds outside Metal Surfaces, Plenum Press, New York (1986).

Ionic radii and diffraction patterns of molten alkali halides

The mean spherical approximation for a fluid of charged hard spheres of different radii is applied to the evaluation of diffraction patterns for the whole family of molten alkali halides. The ionic radii entering the model are determined from the liquid‐state compressibility. The liquid‐state radii are shown to be characteristic temperature‐dependent lengths for each ion through the family of salts, and a good one‐parameter fit of the whole set of compressibilities at each temperature is obtained through the assumption that the radius ratios are those for basic radii yielded by the Born–Mayer theory of alkali halide crystals. The analysis also provides new evidence against the older sets of crystal ionic radii. Calculations of partial structure factors and of x‐ray diffraction patterns are then reported for all the salts and compared with the results of x‐ray and neutron diffraction experiments wherever possible. The model emerges as having semiquantitative value in the prediction of x‐ray diffraction fro...

Polymers, liquid crystals, and low-dimensional solids

This book deals with three related areas having both fundamental and technological interest. In the first part, the objective is to provide a birds eye view on structure in polymeric solids. This is then complemented by a chapter, directly technological in its emphasis, dealing with the influence of processing on polymeric materials. In spite of the technological interest, this leads to some of the current fundamental theory. Part II, concerned with liquid crystals, starts with a discussion of the physics of the various types of material, and concludes with a treatment of optical applications. Again, aspects of the theory are stressed though this part is basically phenomenological in character. In Part III, an account is given first of the use of chemical-bonding arguments in understanding the electronic structure of low-dimensional solids, followed by a comprehensive treatment of the influence of dimen sionality on phase transitions. A brief summary of dielectric screening in low-dimensional solids follows. Space-charge layers are then treated, including semiconductor inversion layers. Effects of limited dimensionality on superconductivity are also emphasized. Part IV concludes the volume with two specialized topics: electronic structure of biopolymers, and topological defects and disordered systems. The Editors wish to acknowledge that this book had its origins in the material presented at a course organized by the International Centre for Theoretical Physics, Trieste.

Structure of liquid alkali metals as electron-ion plasmas

Pscudopotent ial calculations of the stat ic structure factor S(k) of simple liquid nletals involve the construction of an effective ion-ion potent ia l through linear screening of each bare ion by a homogeneous electron gas. The basic assumption made at this step of the theory is tha t the bare electron-ion coupling is weak and the screening clouds of different ions do not interfere with each other. To the extent that this assumption is true, the final result ought to be equivalent to tha t of an elech~on-ion plasma (EIP) approach, in which the structure of the l iquid metal is directly obtained from the structure of a bare ionic p lasma l inearly screened by a homogeneous electron gas. That is (1,~)

Structure of the strongly coupled classical plasma in the self-consistent mean spherical approximation

SummaryAn analytic theory is presented for the static structure factor of the one-component classical plasma at strong couplings. The theory combines the hard-core model of Gillan for short-range correlations in the Coulomb fluid with a semi-empirical representation of intermediate-range correlations, through which the requirement of thermodynamic consistency on the «compressibility» and the known equation of state of the system are satisfied. Excellent agreement is found with the available computer simulation data on the structure of the fluid. The approach becomes inapplicable at intermediate and weak couplings in which effects of penetration in the Coulomb hole of each particle become important.RiassuntoIl lavoro presenta una teoria analitica per il fattore di struttura del plasma classico ad una componente nella situazione di accoppiamento forte. l’effetto di volume escluso, che descrive le correlazioni a corto raggio nel modello già proposto da Gillan, è combinato con una trattazione semiempirica delle correlazioni a distanze intermedie, tramite la quale si assicura la consistenza termodinamica dei risultati e si incorpora l’equazione di stato nota con il metodo Montecarlo. I risultati per la struttura del fluido sono in ottimo accordo con quelli forniti dalla simulazione. Effetti di penetrazione nella buca di correlazione coulombiana di ciascuna particella appaiono importanti in situazioni di accoppiamento intermedio o debole.РезюмеПредлагается аналитическая теория для статического структурного фактора для однокомпонентной классической плазмы при сильных связях. Предложенная теория объединяет модель твердого остова Джилана для корреляций ближнего порядка в кулоновской жидкости с полуэмпирическим представлением корреляций на средних расстояниях, благодаря которым выполняются требование термодинамической непротиворечивости на «сжимаемость» и известное уравнение состояния системы. Получается хорошее согласие с имеющим данными по машинному моделированию структуры жидкости. Предложенный подход становится неприменимым при промежуточных и слабых связях, когда становятся важными эффекты проникновения в кулоновскую дыру каждой частицы.

Restricted primitive model for electrical double layers: Modified HNC theory of density profiles and Monte Carlo study of differential capacitance

Interfacial properties of an ionic fluid next to a uniformly charged planar wall are studied in the restricted primitive model by both theoretical and Monte Carlo methods. The system is a 1:1 fluid of equisized charged hard spheres in a state appropriate to 1 M aqueous electrolyte solutions. The interfacial density profiles of counterions and coions are evaluated by extending the hypernetted chain approximation (HNC) to include the leading bridge diagrams for the wall–ion correlations. The theoretical results compare well with those of grand canonical Monte Carlo computations of Torrie and Valleau over the whole range of surface charge density considered by these authors, thus resolving the earlier disagreement between statistical mechanical theories and simulation data at large charge densities. In view of the importance of the model as a testing ground for theories of the diffuse layer, the Monte Carlo calculations are tested by considering alternative choices for the basic simulation cell and are exten...

Structure of classical liquid of charged hard spheres and point ions

Because of current interest in charged fluids the problem of the structure of a mixture of charged hard spheres of unequal diameters sigma 1 and sigma 2 is studied in the limit sigma 1/ sigma 2 to 0. In particular, the mean spherical model (MSM) has been solved in this limit. The thermodynamics of the mixture is discussed and some typical results for the partial radial distributions are presented. The MSM has the defect in the limiting case sigma 1/ sigma 2 to 0 that the pair correlation function of the point ions always becomes negative at sufficiently short distances. Therefore, to test the predictions of the model, Monte Carlo calculations are presented for this same system for two molten-like states. One of these is just above the expected melting point and the other at an extremely high temperature. In the light of these results, the models relevance to real systems is briefly discussed, CuCl BeF2 and HF each being referred to. An interesting property of the model which we demonstrate is that polymerization can occur.

Liquid alkali metals and alloys as electron-ion plasmas

Abstract Linear screening theory yields expressions for the structure of liquid metals and alloys in terms of the structure of a bare ionic plasma on a rigid background, of the dielectric function of the homogeneous electron gas, and of electron-ion pseudopotentials. The results of such an electron-ion plasma model are examined against experimental data on the structural and thermodynamic properties of the liquid alkali metals and their alloys. The calculations rely on a very accurate theoretical determination of the structure factor of the classical ionic plasma, which embodies its known equation of state and thermodynamic consistency. The model gives a rather accurate account ofthe compressibility of the liquid metal. The main empirical adjustments that are included at finite wavenumber are a choice of the plasma parameter at freezing and a large momentum cutoff of the electron-ion coupling, as suggested by melting-curve data and by a discussion of dynamic criteria for the solid-liquid transition in the alkali metals. The model is then shown to yield very good agreement with experiment for the detailed shape of the structure factor of the liquid metal near freezing, and for its dependence on pressure, temperature and density. A discrepancy with experiment is found in the description of long-wavelength concentration fluctuations in alloys and is attributed to electronic charge transfer between the constituents, which is not included in the model. An estimation of the spinodal curve for the Li-Na alloy is presented in support of this conjecture.

Optical absorption of dilute solutions of metals in molten salts

Abstract The F-centre model for the bound state and the first optical transition of an electron in a metal-molten-salt solution is examined in the high-dilution limit appropriate for comparison with optical absorption data. It is first argued that the model is consistent with recent neutron diffraction and computer simulation data on the structure of pure molten salts, and not incompatible with an Anderson localization model for the electronic conductivity of the solution at higher concentration of metal. A detailed evaluation of the model is presented for the case of a molten salt of equi-sized ions simulating molten KC1. The treatment of the electronic states is patterned after semicontinuum approximations previously applied to the F-centre in ionic crystals, but the equilibrium radius of the electronic cavity and its fluctuations are determined self-consistently from the free energy of the solution. The detailed analysis of this case and the agreement of the results with experiment allow the constructi...

Radius-ratio effects in the structure of fluids of charged hard spheres

The mean spherical model for a binary fluid of charged hard spheres with arbitrary radii has been solved numerically. The results are used to illustrate several aspects of the dependence of the structure of an ionic liquid on the relative sizes of the ionic components.