Strained Semidconductor clusters in sodalite.

Contains fulltext : 104038.pdf (publisher's version ) (Open Access

Binding and migration paths of Au adatoms on the GaAs(001) surface

FWN – Publicaties zonder aanstelling Universiteit Leide

Ab-initio Molecular Dynamics study of electronic and optical properties of silicon quantum wires: Orientational Effects

We analyze the influence of spatial orientation on the optical response of hydrogenated silicon quantum wires. The results are relevant for the interpretation of the optical properties of light emitting porous silicon. We study (111)-oriented wires and compare the present results with those previously obtained within the same theoretical framework for (001)-oriented wires [F. Buda {\it et al.}, {\it Phys. Rev. Lett.} {\bf 69}, 1272, (1992)]. In analogy with the (001)-oriented wires and at variance with crystalline bulk silicon, we find that the (111)-oriented wires exhibit a direct gap at ${\bf k}=0$ whose value is largely enhanced with respect to that found in bulk silicon because of quantum confinement effects. The imaginary part of the dielectric function, for the external field polarized in the direction of the axis of the wires, shows features that, while being qualitatively similar to those observed for the (001) wires, are not present in the bulk. The main conclusion which emerges from the present study is that, if wires a few nanometers large are present in the porous material, they are optically active independently of their specific orientation.Comment: 14 pages (plus 6 figures), Revte

Spontaneous formation and stability of small GaP fullerenes

We report the spontaneous formation of a GaP fullerene cage in ab-initio Molecular Dynamics simulations starting from a bulk fragment. A systematic study of the geometric and electronic properties of neutral and ionized GaP clusters suggests the stability of hetero-fullerenes formed by a compound with zincblend bulk structure. We find that GaP fullerenes up to 28 atoms have high symmetry, closed electronic shells, large HOMO-LUMO energy gaps and do not dissociate when ionized. We compare our results for GaP with those obtained by other groups for the corresponding BN clusters.Comment: To appear on PRL, 4 pages, 1 figure, Late

Further search for a neutral boson with a mass around 9 MeV/c2

Two dedicated experiments on internal pair conversion (IPC) of isoscalar M1 transitions were carried out in order to test a 9 MeV/c2 X-boson scenario. In the 7Li(p,e+e-)8Be reaction at 1.1 MeV proton energy to the predominantly T=0 level at 18.15 MeV, a significant deviation from IPC was observed at large pair correlation angles. In the 11B(d,n e+e-)12C reaction at 1.6 MeV, leading to the 12.71 MeV 1+ level with pure T=0 character, an anomaly was observed at 9 MeV/c2. The compatibility of the results with the scenario is discussed.Comment: 12 pages, 5 figures, 2 table

Calculating energy derivatives for quantum chemistry on a quantum computer

Modeling chemical reactions and complicated molecular systems has been proposed as the `killer application' of a future quantum computer. Accurate calculations of derivatives of molecular eigenenergies are essential towards this end, allowing for geometry optimization, transition state searches, predictions of the response to an applied electric or magnetic field, and molecular dynamics simulations. In this work, we survey methods to calculate energy derivatives, and present two new methods: one based on quantum phase estimation, the other on a low-order response approximation. We calculate asymptotic error bounds and approximate computational scalings for the methods presented. Implementing these methods, we perform the world's first geometry optimization on an experimental quantum processor, estimating the equilibrium bond length of the dihydrogen molecule to within 0.014 Angstrom of the full configuration interaction value. Within the same experiment, we estimate the polarizability of the H2 molecule, finding agreement at the equilibrium bond length to within 0.06 a.u. (2% relative error).Comment: 19 pages, 1 page supplemental, 7 figures. v2 - tidied up and added example to appendice

Adaptation, interaction and urgency:a complex evolutionary economic geography approach to leisure

Local and regional governments in western European peripheral areas aim to spur leisure-led regional development. We explore planning for leisure by applying an evolutionary economic geography (EEG) approach from a complexity perspective. We identify conditions which enable and constrain leisure development and its effects on the region as a whole. This means combining the local level of individual adaptations with the institutional setting and with the regional scale. We examine the Dutch province of Fryslan and explore by means of case study analysis how current leisure development processes can be explained in a complex evolutionary manner. We explore economic novelty as a result of individual adaptations; how such adaptations through interactions create emerging spatial patterns; how these spatial patterns form self-organizing new types of order; and the way this process is dependent on previous paths whilst also creating new pathways. Our findings show that although development is dependent on individual adaptations often stemming from a few actors, for such adaptations to have an effect on the region requires a connectivity between actors and a sense of urgency amongst those actors. Using a complex EEG approach allows us to explain leisure-led regional development as the product of these conditions. This can help planners deal with the complexity and unpredictability of this process, focusing not on a desired end goal as such, but on creating the conditions in which a more autonomous development can take place

Complexity theories and ethnographies in planning for leisure-led regional development

Leisure-led regional development refers to leisure as a mechanism to achieve broad societal goals within a region: economic revenue, employment and service levels but also cultural or conservationist ambitions. Engaging in such leisure-led regional development proves a complex matter. Based on ethnographies of leisure in the Dutch province of Fryslân conducted over a five-year period between 2013 and 2018, this paper argues that combining theoretical understanding of complexity theories with analyses based on both evolutionary and discursive approaches results in enhanced understanding of the interactions shaping uncertainty in leisure development. Results of field observations, interviews, participation and document analysis show that planning for leisure-led regional development should consider autonomous and evolutionary processes, whilst focusing on purposefully influencing the interactions and perspectives of actors in leisure. More precisely, this means shaping the narratives and practices in these institutions which make specific interactions more likely to develop. This can be undertaken by including in planning efforts the individual perspectives and emotions among actors in the regional leisure sector. To cope with uncertainty at the heart of leisure-led regional development, an adaptive strategy should be adopted, both in the planning efforts taken and in how such efforts are monitored and evaluated.</p