Wrocław University of Technology

About: Wrocław University of Technology is a education organization based out in Wrocław, Poland. It is known for research contribution in the topics: Laser & Computer science. The organization has 13115 authors who have published 31279 publications receiving 338694 citations.

Electronically excited states of vitamin B12: benchmark calculations including time-dependent density functional theory and correlated ab initio methods.

Abstract: Time-dependent density functional theory (TD-DFT) and correlated ab initio methods have been applied to explore the electronically excited states of vitamin B(12) (cyanocobalamin or CNCbl). Different experimental techniques have been used to probe the excited states of CNCbl, revealing many issues that remain poorly understood from an electronic structure point of view. Due to its efficient scaling with size, TD-DFT emerges as one of the most practical tools that can be used to study the electronic properties of these fairly complex molecules. However, the description of excited states is strongly dependent on the type of functional used in the calculations. In the present contribution, the choice of a proper functional for vitamin B(12) was evaluated in terms of its agreement with both experimental results and correlated ab initio calculations. Three different functionals, i.e., B3LYP, BP86, and LC-BLYP, were tested. In addition, the effect of the relative contributions of DFT and HF to the exchange-correlation functional was investigated as a function of the range-separation parameter, μ. The issues related to the underestimation of charge-transfer excitation energies by TD-DFT were validated by the Λ diagnostic, which measures the spatial overlap between occupied and virtual orbitals involved in the particular excitation. The nature of the low-lying excited states was also analyzed based on a comparison of TD-DFT and ab initio results. Based on an extensive comparison with experimental results and ab initio benchmark calculations, the BP86 functional was found to be the most appropriate in describing the electronic properties of CNCbl. Finally, an analysis of electronic transitions and reassignment of some excitations were discussed.

Study of mid-infrared laser action in chalcogenide rare earth doped glass with Dy 3+ , Pr 3+ and Tb 3+

Abstract: We present a study of chalcogenide glass fiber lasers doped with Dy3+, Pr3+ or Tb3+ that would operate in the mid-infrared wavelength range. A set of chalcogenide glass samples doped with different concentrations of rare earth ions is fabricated. The modeling parameters are directly extracted from FTIR absorption measurements of the fabricated bulk glass samples using Judd-Ofelt, Fuchtbauer–Ladenburg theory and McCumber theory. The modeling results show that, for all the dopants considered, an efficient mid-infrared laser action is possible if optical losses are kept at the level of 1dB/m or below.

Intrinsic ultracontractivity of the Feynman-Kac semigroup for relativistic stable processes

Abstract: Let X t be the relativistic α-stable process in R d , a ∈ (0, 2), d > α, with infinitesimal generator H (α) 0 = -((-A + m 2/α ) α/2 - m). We study intrinsic ultracontractivity (IU) for the Feynman-Kac semigroup T t for this process with generator H (α) 0 - V, V > 0, V locally bounded. We prove that if lim |x|→∞ V(x) = ∞, then for every t > 0 the operator T t is compact. We consider the class V of potentials V such that V > 0, lim |x|→∞ V(x) = ∞ and V is comparable to the function which is radial, radially nondecreasing and comparable on unit balls. For V in the class V we show that the semigroup T t is IU if and only if lim |x|→∞ V(x)/|x| = ∞. If this condition is satisfied we also obtain sharp estimates of the first eigenfunction Φ 1 for T t . In particular, when V(x) = |x| β , β > 0, then the semigroup T t is IU if and only if β > 1. For β > 1 the first eigenfunction Φ 1 (x) is comparable to.