470 research outputs found
Excitonic effects in the optical properties of CdSe nanowires
Using a first-principle approach beyond density functional theory we
calculate the electronic and optical properties of small diameter CdSe
nanowires.Our results demonstrate how some approximations commonly used in bulk
systems fail at this nano-scale level and how indispensable it is to include
crystal local fields and excitonic effects to predict the unique optical
properties of nanowires. From our results, we then construct a simple model
that describes the optical gap as a function of the diameter of the wire, that
turns out to be in excellent agreement with experiments for intermediate and
large diameters.Comment: submitte
Construction of the B88 exchange-energy functional in two dimensions
We construct a generalized-gradient approximation for the exchange-energy
density of finite two-dimensional systems. Guided by non-empirical principles,
we include the proper small-gradient limit and the proper tail for the
exchange-hole potential. The observed performance is superior to that of the
two-dimensional local-density approximation, which underlines the usefulness of
the approach in practical applications
The eco-geography of the brown shrimp Crangon crangon in Europe
Kooijman, S.A.L.M. [Promotor]Veer, H. van der [Copromotor
On the violation of a local form of the Lieb-Oxford bound
In the framework of density-functional theory, several popular density
functionals for exchange and correlation have been constructed to satisfy a
local form of the Lieb-Oxford bound. In its original global expression, the
bound represents a rigorous lower limit for the indirect Coulomb interaction
energy. Here we employ exact-exchange calculations for the G2 test set to show
that the local form of the bound is violated in an extensive range of both the
dimensionless gradient and the average electron density. Hence, the results
demonstrate the severity in the usage of the local form of the bound in
functional development. On the other hand, our results suggest alternative ways
to construct accurate density functionals for the exchange energy.Comment: (Submitted on 27 April 2012
Mapping the sensitivity of split ring resonators using a localized analyte
Split ring resonator (SRR) based metamaterials have frequently been demonstrated for use as optical sensors of organic materials. This is made possible by matching the wavelength of the SRR plasmonic resonance with a molecular resonance of a specific analyte, which is usually placed on top of the metal structure. However, systematic studies of SRRs that identify the regions that exhibit a high electric field strength are commonly performed using simulations. In this paper we demonstrate that areas of high electric field strength, termed “hot-spots,” can be found by localizing a small quantity of organic analyte at various positions on or near the structure. Furthermore, the sensitivity of the SRR to the localized analyte can be quantified to determine, experimentally, suitable regions for optical sensing
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