Expansion algorithm for the density matrix

A purification algorithm for expanding the single-particle density matrix in terms of the Hamiltonian operator is proposed. The scheme works with a predefined occupation and requires less than half the number of matrix-matrix multiplications compared to existing methods at low (90%) occupancy. The expansion can be used with a fixed chemical potential in which case it is an asymmetric generalization of and a substantial improvement over grand canonical McWeeny purification. It is shown that the computational complexity, measured as number of matrix multiplications, essentially is independent of system size even for metallic materials with a vanishing band gap.Comment: 5 pages, 4 figures, to appear in Phys. Rev.

The Role of Temporary Agency Work in Different Industrial Relations Systems - a Comparison between Germany and the USA

Although temporary agency work has been growing over the last decade, its use differs widely in different industrial relations systems. Drawing on theoretical and empirical insights, propositions are developed on why companies deploy temporary agency work. These propositions are then contrasted with case-study evidence collected in Germany and the USA to analyse the deployment of agency work in two different industrial relations systems and the role that agency work plays in these diverse settings. The main conclusions of the research are that differences in the deployment of temporary agency workers exist with regard to legal regulation and employers' strategies of labour use while similarities exist regarding the supply of agency labour. Copyright Blackwell Publishing Ltd/London School of Economics 2007.