Influence of electron correlations on ground-state properties of III-V semiconductors

Lattice constants and bulk moduli of eleven cubic III-V semiconductors are calculated using an ab initio scheme. Correlation contributions of the valence electrons, in particular, are determined using increments for localized bonds and for pairs and triples of such bonds; individual increments, in turn, are evaluated using the coupled cluster approach with single and double excitations. Core-valence correlation is taken into account by means of a core polarization potential. Combining the results at the correlated level with corresponding Hartree-Fock data, we obtain lattice constants which agree with experiment within an average error of -0.2%; bulk moduli are accurate to +4%. We discuss in detail the influence of the various correlation contributions on lattice constants and bulk moduli.Comment: 4 pages, Latex, no figures, Phys. Rev. B, accepte

Advertising and competition in theory practice and public policy

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This study analyses and compares the theories relating to advertising and competition in economics literature with their operation in the market-place, and with the attitudes and pronouncements of public policy towards advertising and competition. A survey of the main literature in economic theory concerned with advertising and competition includes the theory of value, the theory of the firm, and theories and empirical studies on the effects of advertising and imperfect competition on prices, profits, barriers to entry and product differentiation. Since no general agreement exists on these theories and research, the review is interspersed with criticisms which have been made about specific features of them, and also a short outline of alternative theories which are considered to give a more accurate account of the behaviour of firms in the real world. Consumer behaviour in the market is then studied from three viewpoints: a summary of the major academic theories of consumer behaviour; the results of some empirical research into consumer behaviour; and eight case histories of products and services which show how products are developed and introduced on the market. Finally, the economic theories are compared with the results of the empirical research and the case histories. The theory and practice of advertising and competition is then compared with extracts from the reports of public bodies to illustrate the attitude of public policy towards advertising and competition. The conclusions draw attention to the major discrepancies which appear to exist between theory and practice, and the implications that follow for public policy which seems to be predominantly based on the theory of the firm and the need to eliminate imperfections in the market such as product differentiation, advertising and non-price competition