3,423 research outputs found
Non-Adiabatic Vibrational Damping of Molecular Adsorbates: Insights into Electronic Friction and the Role of Electronic Coherence
We present a perturbation approach rooted in time-dependent
density-functional theory to calculate electron hole (eh)-pair excitation
spectra during the non-adiabatic vibrational damping of adsorbates on metal
surfaces. Our analysis for the benchmark systems CO on Cu(100) and Pt(111)
elucidates the surprisingly strong influence of rather short electronic
coherence times. We demonstrate how in the limit of short electronic coherence
times, as implicitly assumed in prevalent quantum nuclear theories for the
vibrational lifetimes as well as electronic friction, band structure effects
are washed out. Our results suggest that more accurate lifetime or
chemicurrent-like experimental measurements could characterize the electronic
coherence.Comment: Article as accepted for publication in Physical Review Letter
Simulation of Cu-Mg metallic glass: Thermodynamics and Structure
We have obtained effective medium theory (EMT) interatomic potential
parameters suitable for studying Cu-Mg metallic glasses. We present
thermodynamic and structural results from simulations of such glasses over a
range of compositions. We have produced low-temperature configurations by
cooling from the melt at as slow a rate as practical, using constant
temperature and pressure molecular dynamics. During the cooling process we have
carried out thermodynamic analyses based on the temperature dependence of the
enthalpy and its derivative, the specific heat, from which the glass transition
temperature may be determined. We have also carried out structural analyses
using the radial distribution function (RDF) and common neighbor analysis
(CNA). Our analysis suggests that the splitting of the second peak, commonly
associated with metallic glasses, in fact has little to do with the glass
transition itself, but is simply a consequence of the narrowing of peaks
associated with structural features present in the liquid state. In fact the
splitting temperature for the Cu-Cu RDF is well above . The CNA also
highlights a strong similarity between the structure of the intermetallic
alloys and the amorphous alloys of similar composition. We have also
investigated the diffusivity in the supercooled regime. Its temperature
dependence indicates fragile-liquid behavior, typical of binary metallic
glasses. On the other hand, the relatively low specific heat jump of around
indicates apparent strong-liquid behavior, but this can
be explained by the width of the transition due to the high cooling rates.Comment: 12 pages (revtex, two-column), 12 figures, submitted to Phys. Rev.
First-principles statistical mechanics study of the stability of a sub-nanometer thin surface oxide in reactive environments: CO oxidation at Pd(100)
We employ a multiscale modeling approach to study the surface structure and
composition of a Pd(100) model catalyst in reactive environments. Under gas
phase conditions representative of technological CO oxidation (~1 atm, 300-600
K) we find the system on the verge of either stabilizing sub-nanometer thin
oxide structures or CO adlayers at the surface. Under steady-state operation
this suggests the presence or continuous formation and reduction of oxidic
patches at the surface, which could be key to understand the observable
catalytic function.Comment: 4 pages including 2 figures; related publications can be found at
http://www.fhi-berlin.mpg.de/th/th.htm
The European venture capital and private equity country attractiveness index(es)
We calculate composite indexes to compare the attractiveness of 25 European countries for institutional investments into the Venture Capital and Private Equity asset class. To achieve this we use 42 different criteria and propose an aggregation structure that allows for benchmarking on more granular levels. The United Kingdom leads our ranking, followed by Ireland, Denmark, Sweden and Norway. While Germany is slightly above the average European attractiveness level, the scores for France, Italy, Spain, and Greece are rather disappointing. Our analyses reveal that while the United Kingdom is similar to the other European countries with respect to many criteria, there are two major differences which ultimately affect its attractiveness: its investor protection and corporate governance rules; and the size and liquidity of its capital market. The state of the capital market is likewise a proxy for the professionalism of the financial community, deal flow and exit opportunities. We determine a reasonable correlation between our attractiveness index scores and actual Venture Capital and Private Equity fundraising activities and prove the robustness of our calculations. Our findings across all the European countries suggest that while investor protection and capital markets are in fact very important determinants of attractiveness, there are numerous other criteria to consider.Venture Capital; Private Equity; Alternative Asset; International Asset Allocation;
Agassiz, Garman, Albatross, and the Collection of Deep-sea Fishes
The first of Alexander Agassiz’ voyages on the U.S. Fish Commission steamer Albatross in 1891 yielded significant scientific results. This paper reviews the background of the voyage, including the career path that led Agassiz to the back deck of the Albatross. We also give a brief account of the life and work of Samuel Garman. Garman wrote up the ichthyological material from this Albatross voyage in a magnificent book on deep-sea fishes published in 1899. This book was exceptional in its coverage, anatomical detail, and recognition of phylogenetically important morphology
Electronic friction-based vibrational lifetimes of molecular adsorbates: Beyond the independent atom approximation
We assess the accuracy of vibrational damping rates of diatomic adsorbates on
metal surfaces as calculated within the local-density friction approximation
(LDFA). An atoms-in-molecules (AIM) type charge partitioning scheme accounts
for intra-molecular contributions and overcomes the systematic underestimation
of the non-adiabatic losses obtained within the prevalent independent atom
approximation. The quantitative agreement obtained with theoretical and
experimental benchmark data suggests the LDFA-AIM as an efficient and reliable
approach to account for electronic dissipation in ab initio molecular dynamics
simulations of surface chemical reactions.Comment: 5 pages including 2 figure
Effect of surface nanostructure on temperature programmed reaction spectroscopy: First-principles kinetic Monte Carlo simulations of CO oxidation at RuO2(110)
Using the catalytic CO oxidation at RuO2(110) as a showcase, we employ
first-principles kinetic Monte Carlo simulations to illustrate the intricate
effects on temperature programmed reaction spectroscopy data brought about by
the mere correlations between the locations of the active sites at a
nanostructured surface. Even in the absence of lateral interactions, this
nanostructure alone can cause inhomogeneities that cannot be grasped by
prevalent mean-field data analysis procedures, which thus lead to wrong
conclusions on the reactivity of the different surface species.Comment: 4 pages including 3 figures; related publications can be found at
http://www.fhi-berlin.mpg.de/th/th.htm
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