Electronic structure study of vanadium spinels by using density functional theory and dynamical mean field theory

Theoretically, various physical properties of AV$_{2}$O$_{4}$ (A=Zn, Cd and Mg) spinels have been extensively studied for last 15 years. Besides of this, no systematic comparative study has been done for these compounds, where the material specific parameters are used. Here, we report the comparative electronic behaviour of these spinels by using a combination of density functional theory and dynamical mean-field theory, where the self-consistent calculated Coulomb interaction $U$ and Hund's coupling $J$ (determined by Yukawa screening $\lambda$) are used. The main features, such as insulating band gaps ($E_{g}$), degree of itinerancy of V 3$d$ electrons and position of lower Hubbard band are observed for these parameters in these spinels. The calculated values of $E_{g}$ for ZnV$_{2}$O$_{4}$, CdV$_{2}$O$_{4}$ and MgV$_{2}$O$_{4}$ are found to be $\sim$0.9 eV, $\sim$0.95 eV and $\sim$1.15 eV, respectively, where the values of $E_{g}$ are close to experiment for ZnV$_{2}$O$_{4}$ and MgV$_{2}$O$_{4}$. The position of lower Hubbard band are observed around $\sim$-1.05 eV, $\sim$-1.25 eV and $\sim$-1.15 eV for ZnV$_{2}$O$_{4}$, CdV$_{2}$O$_{4}$ and MgV$_{2}$O$_{4}$, respectively, which are also in good agreement with the experimental data for ZnV$_{2}$O$_{4}$. The order of average impurity hybridization function of V site are found to be ZnV$_{2}$O$_{4}$$>$MgV$_{2}$O$_{4}$$>$CdV$_{2}$O$_{4}$. Hence, the degree of localization of V 3$d$ electrons is largest for CdV$_{2}$O$_{4}$ and smallest for ZnV$_{2}$O$_{4}$, which is in accordance with our earlier results. Hence, present work shows the importance of material specific parameters to understand the comparative electronic behaviour of these compounds.Comment: 7 pages, 5 figure

Probabilistic Archetypal Analysis

Archetypal analysis represents a set of observations as convex combinations of pure patterns, or archetypes. The original geometric formulation of finding archetypes by approximating the convex hull of the observations assumes them to be real valued. This, unfortunately, is not compatible with many practical situations. In this paper we revisit archetypal analysis from the basic principles, and propose a probabilistic framework that accommodates other observation types such as integers, binary, and probability vectors. We corroborate the proposed methodology with convincing real-world applications on finding archetypal winter tourists based on binary survey data, archetypal disaster-affected countries based on disaster count data, and document archetypes based on term-frequency data. We also present an appropriate visualization tool to summarize archetypal analysis solution better.Comment: 24 pages; added literature review and visualizatio

Property Type, Size, and REIT Value

This study documents the wide deviation of securitized real estate assets in equity REITs from the value of the underlying commercial properties. A procedure for estimating the net asset value of REITs is developed and the estimates are used to investigate the sources of premiums/discounts from net asset value in a large sample of equity REITs. To avoid measurement error bias, two-way analysis of variance is used to test for differences among size and property-type categories. The results indicate that retail REITs trade at significant premiums relative to the average REIT while warehouse/industrial REITs trade at discounts and small REITs trade at significant discounts while large REITs trade at premiums. The discounts and premiums from net asset value do not translate into higher cash flow yields.