Journal Articles
http://hdl.handle.net/10453/18
2015-07-05T22:08:37ZThe apex of the family tree of protocols: Optimal rates and resource inequalities
http://hdl.handle.net/10453/29110
The apex of the family tree of protocols: Optimal rates and resource inequalities
Datta, Nilanjana; Hsieh, Min-Hsiu
We establish bounds on the maximum entanglement gain and minimum quantum communication cost of the fully quantum Slepian?Wolf (FQSW) protocol in the one-shot regime, which is considered to be at the apex of the existing family tree in quantum information theory. These quantities, which are expressed in terms of smooth min- and max-entropies, reduce to the known rates of quantum communication cost and entanglement gain in the asymptotic independent and identically distributed scenario. We also provide an explicit proof of the optimality of these asymptotic rates. We introduce a resource inequality for the one-shot FQSW protocol, which in conjunction with our results yields achievable one-shot rates of its children protocols. In particular, it yields bounds on the one-shot quantum capacity of a noisy channel in terms of a single entropic quantity, unlike previous bounds. We also obtain an explicit expression for the achievable rate for one-shot state redistribution.
2011-01-01T00:00:00ZA comparative density functional theory investigation of the mechanical and energetic properties of ZnS
http://hdl.handle.net/10453/29102
A comparative density functional theory investigation of the mechanical and energetic properties of ZnS
Feigl, CA; Russo, S; Barnard, A
Using density functional theory, the elastic and energetic properties of zinc sulphide (ZnS) in the zinc blende and wurtzite solid phases have been calculated with several energy functionals within local density and generalised gradient approximations. We report on the plane-wave energy cut-offs (which determine the size of the basis sets) and k-point mesh density required to achieve energy convergence, and discuss the advantages of each functional with respect to computational expense and accuracy. This study provides a means of optimizing the trade-off between accuracy and computational expense due to the choice of energy functional used in further ab initio studies of ZnS systems, and may serve as a guide as to how one may undertake such testing in the case of other materials.
2011-01-01T00:00:00ZSize- and Shape-Dependent Phase Transformations in Wurtzite ZnS Nanostructures
http://hdl.handle.net/10453/29101
Size- and Shape-Dependent Phase Transformations in Wurtzite ZnS Nanostructures
Feigl, CA; Barnard, A; Russo, S
This paper describes the equilibrium morphologies of zinc sulfide nanoparticles in the wurtzite phase as a function of size, determined using ab initio Density Functional Theory (DFT) simulations and a shape-dependent thermodynamic model predicting the Gibbs free energy of a nanoparticle. We investigate the relative stabilities of a variety of nanoparticle shapes based on the wurtzite structure and show how the aspect ratio of wurtzite nanorods moderates the size-dependent phase transformation to the zinc blende phase. We find that while wurtzite nanoparticles are thermodynamically unstable with respect to the low energy rhombic dodecahedron morphology in the zinc blende phase at all sizes, shape- and size-dependent phase transformations occur when other zinc blende morphologies are present. Despite popular synthesis of zinc sulphide nanoparticles in the wurtzite phase, an in-depth thermodynamic study relating to the relative stability of wurtzite shapes and comparison with the zinc blende phase does not exist. Therefore this is the first thermodynamic study describing how shape can determine the solid phase of zinc sulfide nanostructures, which will be of critical importance to experimental applications of nanostructured zinc sulfide, where phase and shape determines properties.
2012-01-01T00:00:00ZMorphological and phase stability of zinc blende, amorphous and mixed core-shell ZnS nanoparticles
http://hdl.handle.net/10453/29103
Morphological and phase stability of zinc blende, amorphous and mixed core-shell ZnS nanoparticles
Barnard, A; Feigl, CA; Russo, S
Zinc sulfide (ZnS) nanoparticles are of interest for their luminescent and catalytic properties which are being considered for the next generation of optical, electronic and photovoltaic devices. However, ZnS nanoparticles undergo reversible and irreversible phase transformations under ambient conditions, so a detailed understanding of the nanomorphology is critical in ensuring these desirable properties can be controlled and maintained. Anticipating the structure and transformations in ZnS nanoparticles experimentally is difficult, since selectivity among competing phases, shapes and sizes is intrinsically linked. Presented here are the results of first principle computer simulations and advanced theoretical modelling used to investigate the relationship between size and shape in determining the crystallinity of ZnS nanoparticles. We find that the equilibrium morphology is characterised by {220} facets, irrespective of the size of the particle, but that the presence of different high energy facets introduced kinetically may significantly influence the zinc blende to amorphous ZnS transformation size, as well as the agglomeration behaviour. In addition to this, we model the relationship between transformation size, morphology and the ratio of crystalline core to amorphous shell and show that at small sizes, a coreshell crystalline/amorphous structure is thermodynamically favourable.
2010-01-01T00:00:00Z