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In this work, we present and apply schemes to determine from first-principles calculations the relevant effective parameters used in phase field theory simulations of battery compounds. In particular, we derive that a consistent free energy density can be obtained by mean-field sampling, which is especially suited for materials with different configurations on a lattice, such as alloys or Li intercalation batteries. In addition, it is demonstrated that mean-field sampling can be performed very effectively with the use of special quasi random structures and that experimentally determined free energy density parameters for ${\mathrm{LiFePO}}_{4}$ are reproduced by density functional theory calculations. The additional computation of interfacial and strain energy parameters allows us to present a consistent phase field parametrization of ${\mathrm{Li}}_{2}{\mathrm{FeSiO}}_{4}$ without relying on experimental data.

We present a measurement of the atmospheric $\nu_e$ spectrum at energies between 0.1 TeV and 100 TeV using data from the first year of the complete IceCube detector. Atmospheric $\nu_e$ originate mainly from the decays of kaons produced in cosmic-ray air showers. This analysis selects 1078 fully contained events in 332 days of livetime, then identifies those consistent with particle showers. A likelihood analysis with improved event selection extends our previous measurement of the conventional $\nu_e$ fluxes to higher energies. The data constrain the conventional $\nu_e$ flux to be $1.3^{+0.4}_{-0.3}$ times a baseline prediction from a Honda's calculation, including the knee of the cosmic-ray spectrum. A fit to the kaon contribution ($\xi$) to the neutrino flux finds a kaon component that is $\xi =1.3^{+0.5}_{-0.4}$ times the baseline value. The fitted/measured prompt neutrino flux from charmed hadron decays strongly depends on the assumed astrophysical flux and shape. If the astrophysical component follows a power law, the result for the prompt flux is $0.0^{+3.0}_{-0.0}$ times a calculated flux based on the work by Enberg, Reno and Sarcevic., Comment: PRD accepted version

Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin-Dahlem, Germany~Received 3 November 1998!Trends in the chemical reactivity of transition-metal surfaces have been studied at the example of thedissociative adsorption of hydrogen on the ~100! surfaces of Rh, Pd, and Ag. Detailed calculations of thesix-dimensional potential-energy surfaces have been performed using density-functional theory. The adsorp-tion dynamics has been investigated by solving the time-independent Schro¨dinger equation via a coupled-channel technique. The results are discussed in the light of current concepts for a reactivity theory.@S0163-1829~99!01720-8#

A tight-binding total-energy (TBTE) method has been developed to interpolate between first-principles results describing the dissociation of molecules at surfaces. The TBTE scheme requires only a relatively small number of ab initio energies as input and gives a reliable global representation of the ab initio potential energy surface to within 0.1 eV accuracy compared to the ab initio results. This approach will open the way to the ab initio molecular dynamics description of reactions invoking many atoms and long time scales that are currently not accessible by first-principles methods.

The presence of sulfur atoms on the Pd(100) surface is known to hinder the dissociative adsorption of hydrogen. Using density-functional theory and the full-potential linear augmented plane-wave method, we investigate the potential energy surface (PES) of the dissociative adsorption of H_2 on the sulfur covered Pd(100) surface. The PES is changed significantly compared to the dissociation on the clean Pd(100) surface, in particular for hydrogen close to the S atoms. While the hydrogen dissociation at the clean Pd(100) surface is non-activated, for the (2x2) sulfur adlayer (coverage Theta_S= 0.25) the dissociation of H_2 is inhibited by energy barriers. Their heights strongly depend on the distance between the hydrogen and sulfur atoms leading to a highly corrugated PES. The largest barriers are in the vicinity of the sulfur atoms due to the strong repulsion between sulfur and hydrogen. Still the hydrogen dissociation on the (2x2) sulfur covered Pd(100) surface is exothermic. Thus the poisoning effect of sulfur adatoms for H_2 dissociation at low sulfur coverage (Theta_S

Ab initio molecular dynamics calculations of deuterium desorbing from Si(100) have been performed in order to monitor the energy redistribution among the various D$_2$ and silicon degrees of freedom during the desorption process. The calculations show that a considerable part of the potential energy at the transition state to desorption is transferred to the silicon lattice. The deuterium molecules leave the surface vibrationally hot and rotationally cold, in agreement with thermal desorption experiments; the mean kinetic energy, however, is larger than found in a laser-induced desorption experiment. We discuss possible reasons for this discrepancy.

The vibrational spectrum of a thiolate-based self-assembled monolayer fabricated by the adsorption of benzylmercaptan on a Au(111) substrate is studied using a combined experimental and theoretical approach employing infrared reflection absorption spectroscopy and density functional theory. The vibrational spectra are derived both using a finite differences approach and from ab initio molecular dynamics simulations at various temperatures. In addition, the possibility of adsorbate-induced reconstructions of the Au(111) substrate is taken into account. It turns out that the measured spectra can only be understood by taking finite temperatures into account.

We have performed a search for muon neutrinos from dark matter annihilation in the center of the Sun with the 79-string configuration of the IceCube neutrino telescope. For the first time, the DeepCore sub-array is included in the analysis, lowering the energy threshold and extending the search to the austral summer. The 317 days of data collected between June 2010 and May 2011 are consistent with the expected background from atmospheric muons and neutrinos. Upper limits are therefore set on the dark matter annihilation rate, with conversions to limits on spin-dependent and spin-independent WIMP-proton cross-sections for WIMP masses in the range 20 - 5000 GeV. These are the most stringent spin-dependent WIMP-proton cross-sections limits to date above 35 GeV., 7 pages, 3 figues

We report the first six-dimensional quantum dynamical calculations of dissociative adsorption and associative desorption. Using a potential energy surface obtained by density functional theory calculations, we show that the increase of the sticking probability with decreasing kinetic energy at low kinetic energies in the system ${\mathrm{H}}_{2}/\mathrm{Pd}(100)$, which is usually attributed to the existence of a molecular adsorption state, is due to dynamical steering. In addition, we examine the influence of rotational motion and orientation of the hydrogen molecule on adsorption and desorption.

We performed high-dimensional quantum dynamical calculations of the dissociative adsorption and associative desorption of hydrogen on Cu(111). The potential energy surface (PES) is obtained from density functional theory calculations. Two regimes of dynamics are found, at low energies sticking is determined by the minimum energy barrier, at high energies by the distribution of barrier heights. Experimental results are well-reproduced qualitatively, but some quantitative discrepancies are identified as well.

Quantum delocalization and correlation effects in one-dimensional chains of bosons are treated using a Bose-Hubbard Hamiltonian including on-site and nearest-neighbor repulsion terms. The parameters were chosen in such a way that the calculations are appropriate for hydrogen atoms adsorbed in the troughs of fcc(110) surfaces. Employing direct diagonalization of the Hamilton matrix for small periodic systems, we find that the hydrogen atoms are always delocalized except for half-filling corresponding to a coverage of $\ensuremath{\rho}=1/2$, where an ordered structure results for small tunnel parameters and sufficiently large nearest-neighbor repulsion, in accordance with experimental findings. For this coverage, a phase diagram as a function of the tunnel parameter and the nearest-neighbor repulsion is determined. Only if the translational invariance of the chain is perturbed, ordered structures for other coverages can be created. Larger systems are studied using the density matrix renormalization group (DMRG) algorithm. Using the finite length version of the DMRG algorithm, we find ordered states also for coverages of $\ensuremath{\rho}=1/3$ and 1/4 which are obviously a consequence of the perturbation caused by the termination of the finite chains.

A search for muon neutrinos from Kaluza-Klein dark matter annihilations in the Sun has been performed with the 22-string configuration of the IceCube neutrino detector using data collected in 104.3 days of live-time in 2007. No excess over the expected atmospheric background has been observed. Upper limits have been obtained on the annihilation rate of captured lightest Kaluza-Klein particle (LKP) WIMPs in the Sun and converted to limits on the LKP-proton cross-sections for LKP masses in the range 250 -- 3000 GeV. These results are the most stringent limits to date on LKP annihilation in the Sun., 6 pages, 5 figures

We employ classical molecular dynamics calculations based on density-functional theory molecule-surface interaction potentials to study H-coverage effects on ${\text{H}}_{2}$ dissociative adsorption on Pd(100). In contrast with one of the basic assumptions of the widely used Langmuir model, we have found that a single isolated H-vacancy is enough to spontaneously dissociate low-energy ${\text{H}}_{2}$ molecules on H-covered Pd(100). We also show that for a given initial coverage (e.g., $\ensuremath{\Theta}=1/2$), the dissociative adsorption probability of low-energy ${\text{H}}_{2}$ molecules can vary by a factor of five depending on the particular arrangement of the H adatoms on the surface.

Strain and coordination effects in the adsorption on early transition metals were studied using density-functional theory. We show that, in contrast to late transition metals, several early transition-metal surfaces with a less than half-filled local $d$ band exhibit lower adsorption energies upon lattice expansion and on low-coordinated sites, in agreement with predictions based on the $d$-band model. This demonstrates that the $d$-band model can be extended to early transition metals. Implications of these results for hydrogen storage materials are discussed.

The relaxation of hot hydrogen atoms upon the dissociative adsorption of ${\mathrm{H}}_{2}$ on Pd(100) was studied by ab initio molecular dynamics simulations based on density functional theory, modeling the full dissociative adsorption process in a consistent manner. In spite of the nonlinear dependence of every single trajectory on the run conditions, on the average it is the energy dissipation to the substrate that determines the mean distance of the two H atoms after adsorption which amounts to three to four lattice units and provides an upper bound for heavier species such as oxygen.

The adsorption behavior of CO on bimetallic Ni/Cu(110) surfaces has been studied experimentally by thermal-desorption spectroscopy and theoretically by density-functional theory (DFT) calculations. The bimetallic surfaces were produced either by evaporation of nickel or by decomposition of $\text{Ni}{(\text{CO})}_{4}$ on Cu(110). Adsorption of CO at 180 K on such a bimetallic surface yields three new adsorption states with adsorption energies between that of CO on clean Cu(110) and clean Ni(110). The new desorption peaks from the bimetallic surface, designated as ${\ensuremath{\beta}}_{1}\text{\ensuremath{-}}{\ensuremath{\beta}}_{3}$, can be observed at 250, 300, and 360 K, respectively. These new states are most pronounced when $\frac{1}{2}$ monolayer of nickel is present on the copper surface. DFT calculations, using the Vienna ab initio simulation package code, were performed to identify the most probable Ni/Cu atomic arrangements at the bimetallic surface to reconcile with the experimental results. It turned out that CO adsorption on nickel dimers consisting of in-surface and adjacent subsurface atoms can best explain the observed experimental data. The result shows that CO adsorption is determined by local (geometric) effects rather than by long-range (electronic) effects. These findings should contribute to a better understanding of tailoring catalytic processes with the help of bimetallic catalysts.

The creation of identical microislands consisting of Ni trimers and multiples thereof on Ru(0001) induced by oxygen adsorption has been observed using scanning tunnelling microscopy. The island formation is caused by an oxygen induced expulsion of Ni atoms or trimers out of the moire-distorted (densified) Ni monolayer. The exceptional stability of the Ni trimers is attributed to oxygen attachment, forming Ni-oxygen composites, as verified by detailed density functional theory calculations. The high density, identical structure, and notable thermal stability of these islands open up new perspectives for the study of the properties of nanostructured surfaces.

We report first-principles calculations on electron transport through ultrathin silicon films between aluminum electrodes. The passivation of interface Si atoms at one side of the film with hydrogen makes the current-voltage characteristics asymmetric with quasirectifying properties. The low conductivity in this case can be explained by the weakened metal-induced gap states due to the passivation. We also demonstrate that the applied bias changes the strength of Fermi-level pinning for the passivated interface.

A neural network (NN) approach is proposed for the representation of six-dimensional ab initio potentialenergy surfaces (PES) for the dissociation of a diatomic molecule at surfaces. We report tests of NN representations that are fitted to six-dimensional analytical PESs for H2 dissociation on the clean and the sulfur covered Pd(100) surfaces. For the present study we use high-dimensional analytical PESs as the basis for the NN training, as this enables us to investigate the influence of phase space sampling on adsorption rates in great detail. We note, however, that these analytical PESs were obtained from detailed density functional theory calculations. When information about the PES is collected only from a few high-symmetric adsorption sites, we find that the obtained adsorption probabilities are not reliable. Thus, intermediate configurations need to be considered as well. However, it is not necessary to map out complete elbow plots above nonsymmetric sites. Our study suggests that only a few additional energies need to be considered in the region of activated systems where the molecular bond breaks. With this understanding, the required number of NN training energies for obtaining a high-quality PES that provides a reliable description of the dissociation and adsorption dynamics is orders of magnitude smaller than the number of total-energy calculations needed in traditional ab initio on the fly molecular dynamics. Our analysis also demonstrates the importance of a reliable, high-dimensional PES to describe reaction rates for dissociative adsorption of molecules at surfaces.

By studying the adsorption of CO on up to 30 layers of Pt deposited on Ru(0001) the influence of surface strain on the adsorption energy has been disentangled from the residual chemical interaction with the substrate. While the electronic influence of the substrate has largely vanished for three Pt layers, the effect of surface strain due to the 2.5% lattice mismatch of Pt and Ru remains initially intact and is only gradually released for $n\ensuremath{\ge}5$ Pt layers. Electronic structure calculations confirm the experimental observations, in particular, the dramatic decrease of the CO adsorption energy on a single Pt layer which is caused by the strong Pt-Ru interlayer coupling.

The local reactivity of Pd overlayers supported by Au has been studied by calculating atomic hydrogen and CO adsorption energies as a microscopic probe. The calculations are based on density functional theory within the generalized gradient approximation. The binding energies show a maximum on two Pd layers on Au, both for the (100) and (111) surfaces. We have furthermore analyzed local trends by considering different adsorption sites on the Pd overlayers. The results can be rationalized within the d-band model if also second-nearest-neighbor interactions and bond-length effects are taken into account.

We present self-consistent density-functional calculations of the adsorption of atomic and molecular hydrogen on the (210) surface of palladium using a plane-wave basis set with optimized ultrasoft pseudopotentials. The layer relaxations of the (210) surface and the preferred adsorption sites for atomic hydrogen adsorption are determined. Furthermore, we show that on the rather open Pd(210) surface a molecular ${\mathrm{H}}_{2}$ adsorption state becomes stabilized by the presence of atomic hydrogen on the surface. This provides a consistent explanation of recent experiments. An analysis of the bonding situation in terms of the local density of states is also presented.

A novel H{sub 2} molecular adsorption state on metal surfaces has been detected by temperature-programmed desorption and electron energy loss spectroscopy experiments of the H{sub 2}/Pd (210) system. The molecular nature of this state has been verified by isotope exchange experiments. This molecular state leads to a decrease of the surface work function while atomic hydrogen on Pd(210) causes an increase. Ab initio total-energy calculations have confirmed all experimental findings. Through these calculations the microscopic nature of this novel molecular adsorption state could be identified; it turns out that this state is stabilized by the presence of atomic hydrogen on the Pd(210) surface.

The rotational and vibrational state distribution of ${\mathrm{D}}_{2}$ molecules desorbing from Pd(100) is determined by tunable vacuum ultraviolet laser ionization spectroscopy. For the deuterium supply a permeation source is used operating at surface temperatures in the range from 400 to 850 K. The molecules are detected in rovibrational states up to ${(v}^{\ensuremath{''}}{,J}^{\ensuremath{''}})=(0,12)$ and (1,8). A significant rotational cooling is observed together with a strong vibrational heating. These experimental results are found to be in good agreement with quantum-mechanical calculations based on an ab initio potential-energy surface. A consistent microscopic picture of the hydrogen reaction dynamics on Pd(100) is established and thus a recent controversy about the application of the principle of detailed balance in the system ${\mathrm{D}}_{2}/\mathrm{Pd}(100)$ can be settled.