Spectral bounds for the Hellmann potential

The method of potential envelopes is used to analyse the bound state spectrum of the Schroedinger Hamiltonian H=-\Delta+V(r), where the Hellmann potential is given by V(r) = -A/r + Be^{-Cr}/r, A and C are positive, and B can be positive or negative. We established simple formulas yielding upper and lower bounds for all the energy eigenvalues.Comment: 9 pages, 2 figures, typos correcte

What is the Role of Legal Systems in Financial Intermediation? Theory and Evidence

We develop a theory and empirical test of how the legal system affects the relationship between venture capitalists and entrepreneurs. The theory uses a double moral hazard framework to show how optimal contracts and investor actions depend on the quality of the legal system. The empirical evidence is based on a sample of European venture capital deals. The main results are that with better legal protection, investors give more non-contractible support and demand more downside protection. These predictions are supported by the empirical analysis. Using a new empirical approach of comparing two sets of fixed-effect regressions, we also find that the investor’s legal system is more important than that of the company in determining investor behavior.Financial Intermediation;Law and Finance;Corporate Governance;Venture Capital

The Importance of Trust for Investment: Evidence From Venture Capital (Revision of DP 2009-43)

We examine the effect of trust on financial investment and contracting decisions in a micro-economic environment where trust is exogenous. Using hand-collected data on European venture capital, we show that the Eurobarometer measure of trust among nations significantly affects investment decisions. This holds even after controlling for investor and company fixed effects, geographic distance, information and transaction costs. The national identity of venture capital firms’ individual partners further contributes to the effect of trust. Education and work experience reduce the effect of trust but do not eliminate it. We also examine the relationship between trust and sophisticated contracts involving contingent control rights and find that, even after controlling for endogeneity, they are complements, not substitutes.Venture Capital;Social Capital;Trust;Financial Contracts;Corporate Governance.

Ab initio Studies of the Possible Magnetism in BN Sheet by Non-magnetic Impurities and Vacancies

We performed first-principles calculations to investigate the possible magnetism induced by the different concentrations of non-magnetic impurities and vacancies in BN sheet. The atoms of Be, B, C, N, O, Al and Si are used to replace either B or N in the systems as impurities. We discussed the changes in density of states as well as the extent of the spatial distributions of the defect states, the possible formation of magnetic moments, the magnitude of the magnetization energies and finally the exchange energies due to the presence of these defects. It is shown that the magnetization energies tend to increase as the concentrations of the defects decreases in most of the defect systems which implies a definite preference of finite magnetic moments. The calculated exchange energies are in general tiny but not completely insignificant for two of the studied defect systems, i.e. one with O impurities for N and the other with B vacancies.Comment: 8 pages, 10 figures, submitted to Phys. Rev.

Linking entanglement and quantum phase transitions via density functional theory

Density functional theory (DFT) is shown to provide a novel conceptual and computational framework for entanglement in interacting many-body quantum systems. DFT can, in particular, shed light on the intriguing relationship between quantum phase transitions and entanglement. We use DFT concepts to express entanglement measures in terms of the first or second derivative of the ground state energy. We illustrate the versatility of the DFT approach via a variety of analytically solvable models. As a further application we discuss entanglement and quantum phase transitions in the case of mean field approximations for realistic models of many-body systems.Comment: 6 pages, 2 figure