Some technical aspects of Cluster Perturbation Theory (CPT) are presented. CPT is an approximation scheme for calculating the oneparticle Green function of the Hubbard model of interacting electrons on a lattice. It proceeds by (i) dividing the lattice into identical clusters and calculating the Green function by exact diagonalization on a given cluster (ii) extending this Green function to the...

A local–orbital based ab initio approach to obtain the Green function for large heterogeneous systems is developed. First a Green function formalism is introduced based on exact diagonalization. Then the self energy is constructed from an incremental scheme, rendering the procedure feasible, while at the same time physical insight into different local correlation contributions is obtained. Subs...

In this paper, the concept and connotation of urban green space and ecosystem service were expatiated, and the research advance in ecosystem service of urban green space was reviewed. The studies of ecosystem service of urban green space in overseas were focused on improving the quality of urban environment, maintaining biodiversity, providing amenity values, and ecosystem management; while in ...

linear green infrastructures along rivers and canals serve different functions: green corridors, or ecological network, maintain biological diversity, improve water quality, and provide areas for fauna and flora to grow and thrive. greenways connect people with landscape resources and serve as recreational areasthat are easy to use and accessible to the greatest number of potential human users....

We discuss conformally covariant differential operators, which under local rescalings of the metric, δσg μν = 2σg , transform according to δσ∆ = r∆σ+(s−r)σ∆ for some r if ∆ is s th order. It is shown that the flat space restrictions of their associated Green functions have forms which are strongly constrained by flat space conformal invariance. The same applies to the variation of the Green fun...