3,451 research outputs found
A universal curve for the design of optimal dielectric elastomer generators: benefits of ceramic filler addition
No full textVibrational properties of tetrahedral amorphous carbon from first principles
No full textWe study the vibrational properties of hydrogenated tetrahedral amorphous carbon from first principles. Our results reproduce the C density of states (DOS) measured by electron energy loss. We decompose the theoretical DOS in terms of vibrational modes of microscopic units. These partial DOS have large overlaps in frequency. Only the region between 1350 and 1600 cm(-1) is covered by a single type of stretching (sp(2)-sp(2)), whose DOS reproduces the experimental visible Raman spectra. We find a linear correlation between CH stretch frequency and CH bond length, and we show that the spreading of CH distances due to the constraints imposed by the C network is an important source of broadening of the CH stretching spectrum. (C) 1999 American Institute of Physics. [S0003-6951(99)02331-1]
Phonon dispersions: Performance of the generalized gradient approximation
No full textBy computing the phonon dispersions of a few selected solids (Si, C, Al, and Cu), within density-functional perturbation theory, we compare the performance of the local density approximation (LDA) with that of the generalized gradient approximations (GGA's) in the form recently proposed by Perdew, Burke, and Ernzerhof [Phys. Rev. Lett. 77, 3865 (1996)]. We find that GGA systematically lowers the frequencies of phonon branches with positive Gruneisen parameters. This effect is correlated with the GGA's expansion of the lattice constant, since GGA phonon frequencies computed at the experimental lattice constants are higher than the corresponding LDA ones. In C, Al, and Cu, LDA and GGA phonon dispersions have similar accuracy with respect to the experimental data. Si is an exception since the LDA phonon dispersions are already in very good agreement with experiment and GGA worsens the comparison. [S0163-1829(99)03339-1]
Adsorption geometry of benzene on Pd(110): Results of first-principles calculations
No full textThe atomic structure of the Pd(110)-c(4 x 2)-benzene system has been determined by means of ab initio slab calculations. A C-2 low-symmetry equilibrium configuration is predicted. The corresponding azimuthal angle theta similar to 11 degrees of the adsorbed molecule is partly due to lateral interactions. The aromatic ring looses planar geometry and the C-H, bonds bend away from the metal. STM images calculated for the C-2 configuration are compatible with recent experimental data
Ab initio study of CO adsorption on Ni(110): Effects on surface magnetism at low coverage
No full textThe magnetization of the Ni(110) surface is explored as a function of the CO coverage by means of periodic slab calculations within density-functional theory. The in-plane inspection of the spin density corresponding to the surface layer exhibits a CO-induced decrease in the Ni-atom magnetic moments that is limited to the atoms directly involved in the chemisorption bond. This decrease is due to interactions between the metal states and the CO orbitals that increase the population of the spin-down metal states within the outermost layer and decrease that of the corresponding spin-up ones
CO adsorbed on Cu(001): A comparison between local density approximation and Perdew, Burke, and Ernezerhof generalized gradient approximation
No full textAdsorption energetics, structural and vibrational properties of the Cu(001)-c(2 X 2)-CO system are studied with periodic slab calculations within density functional theory in the local density (LDA) and generalized gradient (GGA) approximations by using ultrasoft pseudopotentials. The recent expression of Perdew, Burke, and Ernzerhof (PBE) has been used as the GGA functional [Phys. Rev; Lett. 77, 3865 (1996)]. The fully relaxed geometry of the system is determined for different adsorption sites,of the CO molecule; unlike LDA, PBE-GGA predicts correctly the on-top adsorption site of the molecule. C-O and Cu-CO bond lengths, stretching frequencies, Cu-layer displacements, chemisorption energies, and work functions are computed under both approximations and are compared to the experimental values. LDA. gives accurate,values for the C-O equilibrium distance and the corresponding stretching frequency, while PBE-GGA better describes the adsorption bond and all the remaining properties. (C) 2001 American Institute of Physics
Etica e mondo del lavoro.Organizzazioni positive, azione, responsabilità
No full textLa riflessione su etica e mondo del lavoro, condotta presso l'Università di Padova nell'ambito delle scienze filosofiche e psicologiche, si arricchisce di un nuovo contributo che fa seguito alla pubblicazione di Etica e mondo del lavoro. Razionalità, modelli, buone prassi (FrancoAngeli, 2016). I contenuti portanti di questo secondo volume sono la "positività" delle organizzazioni, l'azione e la responsabilità, la valorizzazione della persona nelle sue componenti valoriali, relazionali e applicative.
Il tema di base per le due dimensioni principali della trattazione - l'impegno vissuto dal singolo e le finalità e i contenuti dell'operare organizzativo - consiste nella consapevolezza che l'agire individuale e collettivo nelle diverse attività lavorative fa sì che ogni essere umano possa realizzarsi sempre più propriamente e compiutamente.
La dignità di ogni lavoro e la sua "trascendenza" rispetto agli impegni sia quotidiani sia protratti nel tempo innervano e danno senso comune ai diversi contributi, in una chiave di costante integrazione fra le diverse discipline
Il mondo del lavoro fra valori e normative. Risultati di un'indagine empirica sulla relazione tra Employee Assistance Programs - EAPs e benessere organizzativo.
No full textIl contributo si propone di prendere in esame le normative oggi vigenti in tema di promozione del benessere organizzativo e delle performance lavorative, di tutela della salute e di contrasto dello stress lavoro-correlato, cogliendone gli aspetti sia valoriali che applicativi. Si descrivono i principali risultati di un'indagine empirica recentemente realizzata, che mostrano una elevata correlazione fra gli interventi condotti dalle organizzazioni per migliorare contesti e contenuti del lavoro (Employee Assistance Programs - EAPs) e i risultati percepiti dai lavoratori in termini di benessere organizzativo, coinvolgimento personale e soddisfazione professionale
Wannier and Bloch orbital computation of the nonlinear susceptibility
No full textWe present a method to compute high-order derivatives of the total energy of a periodic solid with respect to a uniform electric field. We apply the 2n + 1 theorem to a recently introduced total energy functional which uses a Wannier representation for the electronic orbitals and we find an expression for the static nonlinear susceptibility which is much simpler than the one obtained by standard perturbative expansions. We show that the zero-field expression of the nonlinear susceptibility can be rewritten in a Bloch representation. We test numerically the validity of our approach with a 1D model Hamiltonian
First-principles Wannier functions of silicon and gallium arsenide
No full textWe present a self-consistent, real-space calculation of the Wannier functions of Si and GaAs within density-functional theory. We minimize the total-energy functional with respect to orbitals which behave as Wannier functions under crystal translations and, at the minimum, are orthogonal. The Wannier functions are used to calculate the total energy, lattice constant, bulk modulus, and the frequency of the zone-center TO phonon of the two semiconductors with the accuracy required in ab initio calculations. Furthermore, the centers of the Wannier functions are used to compute the macroscopic polarization of Si and GaAs in zero electric field. The effective charges of GaAs, obtained by finite differentiation of the polarization, agree with the results of linear-response theory
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