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Structural and electronic properties of SrZrO3 and Sr(Ti,Zr) O3 alloys
Using hybrid density functional calculations, we study the electronic and structural properties of SrZrO3 and ordered Sr(Ti,Zr)O3 alloys. Calculations were performed for the ground-state orthorhombic (Pnma) and high-temperature cubic (Pm3m) phases of SrZrO3. The variation of the lattice parameters and band gaps with Ti addition was studied using ordered SrTixZr1-xO3 structures with x=0, 0.25, 0.5, 0.75, and 1. As Ti is added to SrZrO3, the lattice parameter is reduced and closely follows Vegard's law. On the other hand, the band gap shows a large bowing and is highly sensitive to the Ti distribution. For x=0.5, we find that arranging the Ti and Zr atoms into a 1Ă—1SrZrO3/SrTiO3 superlattice along the [001] direction leads to interesting properties, including a highly dispersive single band at the conduction-band minimum (CBM), which is absent in both parent compounds, and a band gap close to that of pure SrTiO3. These features are explained by the splitting of the lowest three conduction-band states due to the reduced symmetry of the superlattice, lowering the band originating from the in-plane Ti 3dxy orbitals. The lifting of the t2g orbital degeneracy around the CBM suppresses scattering due to electron-phonon interactions. Our results demonstrate how short-period SrZrO3/SrTiO3 superlattices could be exploited to engineer the band structure and improve carrier mobility compared to bulk SrTiO3
Exploring, tailoring, and traversing the solution landscape of a phase-shaped CARS process
Pulse shaping techniques are used to improve the selectivity of broadband CARS experiments, and to reject the overwhelming background. Knowledge about the fitness landscape and the capability of tailoring it is crucial for both fundamental insight and performing an efficient optimization of phase shapes. We use an evolutionary algorithm to find the optimal spectral phase of the broadband pump and probe beams in a background-suppressed shaped CARS process. We then investigate the shapes, symmetries, and topologies of the landscape contour lines around the optimal solution and also around the point corresponding to zero phase. We demonstrate the significance of the employed phase bases in achieving convex contour lines, suppressed local optima, and high optimization fitness with a few (and even a single) optimization parameter
Safety and efficacy of eculizumab in pediatric patients with aHUS, with or without baseline dialysis
Interatomic potentials for mixed oxide (MOX) nuclear fuels
We extend our recently developed interatomic potentials for UO_{2} to the
mixed oxide fuel system (U,Pu,Np)O_{2}. We do so by fitting against an
extensive database of ab initio results as well as to experimental
measurements. The applicability of these interactions to a variety of mixed
environments beyond the fitting domain is also assessed. The employed formalism
makes these potentials applicable across all interatomic distances without the
need for any ambiguous splining to the well-established short-range
Ziegler-Biersack-Littmark universal pair potential. We therefore expect these
to be reliable potentials for carrying out damage simulations (and Molecular
Dynamics simulations in general) in nuclear fuels of varying compositions for
all relevant atomic collision energies
Generating derivative structures: Algorithm and applications
We present an algorithm for generating all derivative superstructures--for
arbitrary parent structures and for any number of atom types. This algorithm
enumerates superlattices and atomic configurations in a geometry-independent
way. The key concept is to use the quotient group associated with each
superlattice to determine all unique atomic configurations. The run time of the
algorithm scales linearly with the number of unique structures found. We show
several applications demonstrating how the algorithm can be used in materials
design problems. We predict an altogether new crystal structure in Cd-Pt and
Pd-Pt, and several new ground states in Pd-rich and Pt-rich binary systems
Phonon-assisted optical absorption in silicon from first principles
The phonon-assisted interband optical absorption spectrum of silicon is
calculated at the quasiparticle level entirely from first principles. We make
use of the Wannier interpolation formalism to determine the quasiparticle
energies, as well as the optical transition and electron-phonon coupling matrix
elements, on fine grids in the Brillouin zone. The calculated spectrum near the
onset of indirect absorption is in very good agreement with experimental
measurements for a range of temperatures. Moreover, our method can accurately
determine the optical absorption spectrum of silicon in the visible range, an
important process for optoelectronic and photovoltaic applications that cannot
be addressed with simple models. The computational formalism is quite general
and can be used to understand the phonon-assisted absorption processes in
general
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