Spin state transition in LaCoO3 by variational cluster approximation

The variational cluster approximation is applied to the calculation of thermodynamical quantities and single-particle spectra of LaCoO3. Trial self-energies and the numerical value of the Luttinger-Ward functional are obtained by exact diagonalization of a CoO6 cluster. The VCA correctly predicts LaCoO3 as a paramagnetic insulator and a gradual and relatively smooth increase of the occupation of high-spin Co3+ ions causes the temperature dependence of entropy and magnetic susceptibility. The single particle spectral function agrees well with experiment, the experimentally observed temperature dependence of photoelectron spectra is reproduced satisfactorily. Remaining discrepancies with experiment highlight the importance of spin orbit coupling and local lattice relaxation.Comment: Revtex file with 10 eps figure

Designing an effective evaluation model for the South African Department of Agriculture

Governments are under increasing pressure to deliver results. Therefore, it is important to evaluate the effectiveness, efficiency and relevance of the public service in implementing policies and programmes for social betterment. Without such evaluations, it is difficult to ensure that evidence is integrated into policy and used in practice due to lack of generalizability and learning. This paper focuses on (1) the knowledge that is relevant to understand evaluation influence, (2) the possible conceptual frameworks that enable understanding of the evaluation implementation process, (3) possible models of the process of organizational evaluation, and (4) the main ways of intervening to increase influence. The context for analysis is the South African Department of Agriculture.Evaluation, Evaluation Influence, Policy, Programmes, South Africa, Political Economy, Research Methods/ Statistical Methods,

Correlated band structure of NiO, CoO and MnO by variational cluster approximation

The variational cluster approximation proposed by Potthoff is applied to the calculation of the single-particle spectral function of the transition metal oxides MnO, CoO and NiO. Trial self-energies and the numerical value of the Luttinger-Ward functional are obtained by exact diagonalization of a TMO6-cluster. The single-particle parameters of this cluster serve as variational parameters to construct a stationary point of the grand potential of the lattice system. The stationary point is found by a crossover procedure which allows to go continuously from an array of disconnected clusters to the lattice system. The self-energy is found to contain irrelevant degrees of freedom which have marginal impact on the grand potential and which need to be excluded to obtain meaningful results. The obtained spectral functions are in good agreement with experimental data.Comment: 14 pages, 17 figure

One little Lebanese cucumber is not going to break the bank: Price in the choice of fresh fruits and vegetables

This paper reports on empirical research into individual consumer behaviour in the context of fresh fruit and vegetable purchases. The discussion draws on research results from two studies conducted around the actual shopping process. The findings suggest that consumers’ price response behaviour may not be consistent with that predicted by economic theory and that this could be significant at the aggregate level. The existence of ‘acceptable price ranges’ points to the presence of price thresholds within which consumers are relatively insensitive to price movements. Also of relevance is that the primary influence of the budget constraint may be at a broader level rather than at the level of choosing particular products.Demand and Price Analysis, Food Consumption/Nutrition/Food Safety,