Van der Waals interactions in DFT made easy by Wannier functions

Ubiquitous Van der Waals interactions between atoms and molecules are important for many molecular and solid structures. These systems are often studied from first principles using the Density Functional Theory (DFT). However, the commonly used DFT functionals fail to capture the essence of Van der Waals effects. Many attempts to correct for this problem have been proposed, which are not completely satisfactory because they are either very complex and computationally expensive or have a basic semiempirical character. We here describe a novel approach, based on the use of the Maximally-Localized Wannier functions, that appears to be promising, being simple, efficient, accurate, and transferable (charge polarization effects are naturally included). The results of test applications are presented.Comment: submitted to Phys. Rev. Let

Factors influencing the distribution of charge in polar nanocrystals

We perform first-principles calculations of wurtzite GaAs nanorods to explore the factors determining charge distributions in polar nanostructures. We show that both the direction and magnitude of the dipole moment $\mathbf{d}$ of a nanorod, and its electic field, depend sensitively on how its surfaces are terminated and do not depend strongly on the spontaneous polarization of the underlying lattice. We identify two physical mechanisms by which $\mathbf{d}$ is controlled by the surface termination, and we show that the excess charge on the nanorod ends is not strongly localized. We discuss the implications of these results for tuning nanocrystal properties, and for their growth and assembly.Comment: Accepted for publication in Phys. Rev. B Rapid Communication

The assessment of the flow requirements for upstream migration of salmonids in some rivers of North West England

This is the assessment of the flow requirements for upstream migration of salmonids in some rivers of North West England produced by the North West Water Authority in 1985. This report focuses on the automatic fish counters operating on the resistivity principle used for several years in North West England. This report aims to investigate the flow requirements for upstream migration of salmon and migratory trout. The data obtained confirmed that during summer months most fish movement occurs in the higher range of the available flows, but the migration flow range varied from year to year, depending on prevailing river levels. Of the other environmental variables measured, only water temperature and incident light intensity appear to have any direct association with fish movement. Information on migration flow ranges were used in conjunction with computer simulations of the effects of abstraction proposals on historical flows to assess the implications of these proposals for migratory fish

Projector self-consistent DFT+U using non-orthogonal generalized Wannier functions

We present a formulation of the density-functional theory + Hubbard model (DFT+U) method that is self-consistent over the choice of Hubbard projectors used to define the correlated subspaces. In order to overcome the arbitrariness in this choice, we propose the use of non-orthogonal generalized Wannier functions (NGWFs) as projectors for the DFT+U correction. We iteratively refine these NGWF projectors and, hence, the DFT+U functional, such that the correlated subspaces are fully self-consistent with the DFT+U ground-state. We discuss the convergence characteristics of this algorithm and compare ground-state properties thus computed with those calculated using hydrogenic projectors. Our approach is implemented within, but not restricted to, a linear-scaling DFT framework, opening the path to DFT+U calculations on systems of unprecedented size.Comment: 4 pages, 3 figures. This version (v2) matches that accepted for Physical Review B Rapid Communications on 26th July 201

MARKETING PREMIUM FOOD PRODUCTS IN EMERGING ECONOMIES: THE CASE OF MACEDONIAN CHEESE

Developing food products with higher standards or brands in newly emerging markets presents a challenge to processors. This study focused on attributes that may increase cheese demand in Macedonian. Demand for higher quality, taste, consistency and certified "safe" cheese at premiums is relatively high. Income, region, shopping behavior and various other demographics all delineate potential consumers of premium cheese.Marketing,