71 research outputs found
Stability and electronic structure of the SrTiO(110) polar surfaces by first principles calculations
The electronic and atomic structure of several terminations of
the (110) polar orientation of SrTiO surface are systematically studied by
first-principles calculations. The electronic structure of the two
stoichiometric SrTiO- and O-terminations are characterized by marked
differences with respect to the bulk, as a consequence of the polarity
compensation. In the former, the Fermi level is located at the bottom of the
conduction band, while in the latter the formation of a peroxo bond between the
two surface oxygens results in a small-gap insulating surface with states in
the gap of the bulk projected band structure. We also consider three non
stoichiometric terminations with TiO, Sr and O compositions, respectively, in
the outermost atomic layer, which automatically allows the surface to be free
from any macroscopic polarization. They are all insulating. The cleavage and
surface energies of the five terminations are computed and compared, taking
into account the influence of the chemical environment as a function of the
relative richness in O and Sr. From our calculations it appears that some (110)
faces can even compete with the TiO and SrO terminations of the (100)
cleavage surface: in particular, the (110)-TiO termination is stable in Sr-poor
conditions, the (110)-Sr one in simultaneously O- and Sr-rich environments. The
available experimental data are compared to the outcomes of our calculations
and discussed.Comment: accepted for publication in Phys. Rev.
Il Colle e l'"Alto Luogo di Tanit" : campagne 2007-2011 : lo scavo del versante settentrionale : le evidenze strutturali pre romane
When Quantum Fluctuations Meet Structural Instabilities: The Isotope- and Pressure-Induced Phase Transition in the Quantum Paraelectric NaOH
Anhydrous sodium hydroxide, a common and structurally simple compound, shows
spectacular isotope effects: NaOD undergoes a first-order transition, which is
absent in NaOH. By combining ab initio electronic structure calculations with
path integrals, we show that NaOH is an unusual example of a quantum
paraelectric: zero-point quantum fluctuations stretch the weak hydrogen bonds
(HBs) until they become unstable and break. By strengthening HBs via isotope
substitution or applied pressure, the system can be driven down to a
broken-symmetry antiferroelectric phase. We also provide a simple quantitative
criterion for HB breaking in layered crystals and show that nuclear quantum
effects are crucial in paraelectric to ferroelectric transitions in
hydrogen-bonded hydroxides
Numerical atomic orbitals for linear scaling
The performance of basis sets made of numerical atomic orbitals is explored
in density-functional calculations of solids and molecules. With the aim of
optimizing basis quality while maintaining strict localization of the orbitals,
as needed for linear-scaling calculations, several schemes have been tried. The
best performance is obtained for the basis sets generated according to a new
scheme presented here, a flexibilization of previous proposals. The basis sets
are tested versus converged plane-wave calculations on a significant variety of
systems, including covalent, ionic and metallic. Satisfactory convergence
(deviations significantly smaller than the accuracy of the underlying theory)
is obtained for reasonably small basis sizes, with a clear improvement over
previous schemes. The transferability of the obtained basis sets is tested in
several cases and it is found to be satisfactory as well.Comment: 9 pages with 2 encapsulated postscript figures, submitted to Phys.
Rev.
First Case of Patient With Two Homozygous Mutations in MYD88 and CARD9 Genes Presenting With Pyogenic Bacterial Infections, Elevated IgE, and Persistent EBV Viremia
We described for the first time a female patient with the simultaneous presence of two homozygous mutations in MYD88 and CARD9 genes presenting with pyogenic bacterial infections, elevated IgE, and persistent EBV viremia. In addition to defective TLR/IL1R-signaling, we described novel functional alterations into the myeloid compartment. In particular, we demonstrated a defective production of reactive oxygen species exclusively in monocytes upon E. coli stimulation, the inability of immature mono-derived DCs (iDCs) to differentiate into mature DCs (mDCs) and the incapacity of mono-derived macrophages (MDMs) to resolve BCG infection in vitro. Our data do not provide any evidence for digenic inheritance in our patient, but rather for the association of two monogenic disorders. This case illustrates the importance of using next generation sequencing (NGS) to determine the most accurate and early diagnosis in atypical clinical and immunological phenotypes, and with particular concern in consanguineous families. Indeed, besides the increased susceptibility to recurrent invasive pyogenic bacterial infections due to MYD88 deficiency, the identification of CARD9 mutations underline the risk of developing invasive fungal infections emphasizing the careful monitoring for the occurrence of fungal infection and the opportunity of long-term antifungal prophylaxis
Strategies for preventing group B streptococcal infections in newborns: A nation-wide survey of Italian policies
Pseudopotentials plane waves - Projector augmented waves: A primer
We review the basic concepts underlying the use of plane wave basis sets for the implementation of Density Functional Theory, including pseudopotentials (norm-conserving or ultra-soft pseudopotentials), or their refinement, the projector-augmented wave method. Explicit plane wave expressions for the Hamiltonian and electronic energy based on norm-conserving pseudopotentials are presented
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