On-surface and Subsurface Adsorption of Oxygen on Stepped Ag(210) and Ag(410) Surfaces

The adsorption of atomic oxygen and its inclusion into subsurface sites on Ag(210) and Ag(410) surfaces have been investigated using density functional theory. We find that--in the absence of adatoms on the first metal layer--subsurface adsorption results in strong lattice distortion which makes it energetically unfavoured. However subsurface sites are significantly stabilised when a sufficient amount of O adatoms is present on the surface. At high enough O coverage on the Ag(210) surface the mixed on-surface + subsurface O adsorption is energetically favoured with respect to the on-surface only adsorption. Instead, on the Ag(410) surface, at the coverage we have considered (3/8 ML), the existence of stable terrace sites makes the subsurface O incorporation less favourable. These findings are compatible with the results of recent HREEL experiments which have actually motivated this work.Comment: 8 pages, 4 figures and 1 tabl

Electron-vibration coupling constants in positively charged fullerene

Recent experiments have shown that C60 can be positively field-doped. In that state, fullerene exhibits a higher resistivity and a higher superconducting temperature than the corresponding negatively doped state. A strong intramolecular hole-phonon coupling, connected with the Jahn-Teller effect of the isolated positive ion, is expected to be important for both properties, but the actual coupling strengths are so far unknown. Based on density functional calculations, we determine the linear couplings of the two a_g, six g_g, and eight h_g vibrational modes to the H_u HOMO level of the C60 molecule. The couplings predict a D_5 distortion, and an H_u vibronic ground state for C60^+. They are also used to generate the dimensionless coupling constant which controls the superconductivity and the phonon contribution to the electrical resistivity in the crystalline phase. We find that is 1.4 times larger in positively-charged C60 than in the negatively-doped case. These results are discussed in the context of the available transport data and superconducting temperatures. The role of higher orbital degeneracy in superconductivity is also addressed.Comment: 22 pages - 3 figures. This revision includes few punctuation corrections from proofreadin

High-order density-matrix perturbation theory

We present a simple formalism for the calculation of the derivatives of the electronic density matrix at any order, within density functional theory. Our approach, contrary to previous ones, is not based on the perturbative expansion of the Kohn-Sham wavefunctions. It has the following advantages: (i) it allows a simple derivation for the expression for the high order derivatives of the density matrix; (ii) in extended insulators, the treatment of uniform-electric-field perturbations and of the polarization derivatives is straightforward.Comment: 4 page

First-principles study of lattice instabilities in the ferromagnetic martensite Ni2_2MnGa

The phonon dispersion relations and elastic constants for ferromagnetic Ni$_2$MnGa in the cubic and tetragonally distorted Heusler structures are computed using density-functional and density-functional perturbation theory within the spin-polarized generalized-gradient approximation. For $0.9<c/a<1.06$, the TA$_2$ tranverse acoustic branch along $[110]$ and symmetry-related directions displays a dynamical instability at a wavevector that depends on $c/a$. Through examination of the Fermi-surface nesting and electron-phonon coupling, this is identified as a Kohn anomaly. In the parent cubic phase the computed tetragonal shear elastic constant, C$^\prime$=(C$_{11}-$C$_{12}$)/2, is close to zero, indicating a marginal elastic instability towards a uniform tetragonal distortion. We conclude that the cubic Heusler structure is unstable against a family of energy-lowering distortions produced by the coupling between a uniform tetragonal distortion and the corresponding $[110]$ modulation. The computed relation between the $c/a$ ratio and the modulation wavevector is in excellent agreement with structural data on the premartensitic ($c/a$ = 1) and martensitic ($c/a$ = 0.94) phases of Ni$_2$MnGa.Comment: submitted to Phys. Rev.

Targeted delivery of cytotoxic drugs: Challenges, opportunities and new developments

Cytotoxic drugs, which are commonly used for the pharmacotherapy of many forms of cancer, often cause substantial toxicity to the patient without being able to induce long-lasting remissions. Ligands specific to accessible tumor-associated targets, capable of selective localization at the neoplastic site, may facilitate the preferential delivery of anti-cancer drugs, boosting activity and helping spare normal organs. In this article, we present a critical analysis of the limitation of conventional anti-cancer drugs and we contrast monoclonal antibodies and small organic ligands, as vehicles for pharmacodelivery applications

Is workaholism associated with inflammatory response? The moderating role of work engagement

The aim of this study was to investigate the association between two different forms of heavy work investment, namely workaholism and work engagement, and serum levels of the proinflammatory cytokine interleukin-17 (IL-17), a possible biomarker of stress. Given the different motivational underpinnings and outcomes of workaholism and work engagement and drawing on the allostatic load and the effort-recovery models, we hypothesized that workaholism is positively associated with IL-17, and that work engagement buffers this association. Workers in an Italian healthcare organization (88 females and 31 males) completed a self-report questionnaire, and then underwent blood sample collection. Data were analysed using moderated multiple regression. Results showed that workaholism was positively associated with IL-17, controlling for the effect of gender, age, and body mass index. Work engagement buffered this association, which was nonsignificant when work engagement was high. To reduce the risk of future health complaints, interventions should be aimed at preventing workaholism and promoting work engagement

Simulation of electron energy loss spectra with the turboEELS and thermo-pw codes

For some materials like noble metals, electron energy loss spectra have a complex structure that makes them difficult to analyze without the help of ab initio calculations. Various theoretical approaches can be used for this purpose, among which the time-dependent density functional perturbation theory (TDDFPT) which has been widely used to study plasmons in a number of bulk and surface systems. In the present paper we present a comparison of the results and performance of two different numerical implementations of TDDFPT: the Sternheimer and Liouville-Lanczos methods. The former approach is implemented in the thermo-pw module and the latter one in the turboEELS code of the QUANTUM ESPRESSO package for electronic structure calculations. In the present paper a comparison is made for bulk bismuth, a semimetal, taking into account spin-orbit coupling, as well as for bulk gold, a noble metal. We show that for these two examples, both codes gives identical results and the turboEELS code has a better performance than the thermo-pw code, and point out in which cases the usage of thermo-pw alone or of both codes can be advantageous

Spontaneous polarization and piezoelectric constants of III-V nitrides

The spontaneous polarization, dynamical Born charges, and piezoelectric constants of the III-V nitrides AlN, GaN, and InN are studied ab initio using the Berry phase approach to polarization in solids. The piezoelectric constants are found to be up 10 times larger than in conventional III-V's and II-VI's, and comparable to those of ZnO. Further properties at variance with those of conventional III-V compounds are the sign of the piezoelectric constants (positive as in II-VI's) and the very large spontaneous polarization.Comment: RevTeX 4 pages, improved upon revie