On the Impact of Solvation on a Au/TiO2 Nanocatalyst in Contact with Water

Water, the ubiquitous solvent, is also prominent in forming liquid solid interfaces with catalytically active surfaces, in particular with promoted oxides. We study the complex interface of a gold nanocatalyst, pinned by an F center on titania support, and water. The ab initio simulations uncover the microscopic details of solvent-induced charge rearrangements at the metal particle. Water is found to stabilize charge states differently from the gas phase as a result of structure specific charge transfer from to the solvent, thus altering surface reactivity. The metal cluster is shown to feature both cationic and anionic solvation, depending on fluctuation and polarization effects in the liquid, which creates novel active sites. These observations open up an avenue toward solvent engineering in liquid-phase heterogeneous catalysis

FILOSOFÍA Y ESCRITURA EN EL PLATÓN DE LEO STRAUSS

Lo que Leo Strauss define como «filosofía política clásica» parece coincidir con la cuestión planteada por la propia filosofía de su relación con la comunidad política, pensada como el «lugar» original de la reflexión sobre las relaciones humanas. En virtud del problema que determina su investigación, la «filosofía política clásica» se caracteriza por una relación directa con la vida política1. De esta premisa podría concluirse que el «objeto» de la filosofía política, al menos tal y como parecen entenderla Sócrates, Platón y Aristóteles, sería el propio filósofo como miembro de una comunidad política o, menor dicho, el problema de la acción del filósofo en esa comunidad. Habría que advertir, además, que la reflexión straussiana sobre el pensamiento político se concentra específicamente en la obra de Platón. La figura del filósofo que proponen los Diálogos es la de Sócrates; por esta razón, podría decirse que, para Strauss, el problema de la filosofía política de Platón equivale al «problema de Sócrates». Según este presupuesto, el tratamiento straussiano del pensamiento de Platón está estrechamente ligado a la identificación precisa de la «figura de Sócrates»

Ideal, Defective, and Gold--Promoted Rutile TiO2(110) Surfaces: Structures, Energies, Dynamics, and Thermodynamics from PBE+U

Extensive first principles calculations are carried out to investigate gold-promoted TiO2(110) surfaces in terms of structure optimizations, electronic structure analyses, ab initio thermodynamics calculations of surface phase diagrams, and ab initio molecular dynamics simulations. All computations rely on density functional theory in the generalized gradient approximation (PBE) and account for on-site Coulomb interactions via inclusion of a Hubbard correction, PBE+U, where U is computed from linear response theory. This approach is validated by investigating the interaction between TiO2(110) surfaces and typical probe species (H, H2O, CO). Relaxed structures and binding energies are compared to both data from the literature and plain PBE results. The main focus of the study is on the properties of gold-promoted titania surfaces and their interactions with CO. Both PBE+U and PBE optimized structures of Au adatoms adsorbed on stoichiometric and reduced TiO2 surfaces are computed, along with their electronic structure. The charge rearrangement induced by the adsorbates at the metal/oxide contact are also analyzed and discussed. By performing PBE+U ab initio molecular dynamics simulations, it is demonstrated that the diffusion of Au adatoms on the stoichiometric surface is highly anisotropic. The metal atoms migrate either along the top of the bridging oxygen rows, or around the area between these rows, from one bridging position to the next along the [001] direction. Approximate ab initio thermodynamics predicts that under O-rich conditions, structures obtained by substituting a Ti5c atom with an Au atom are thermodynamically stable over a wide range of temperatures and pressures.Comment: 20 pages, 12 figures, accepted for publication in Phys. Rev.

Ab-Initio Molecular Dynamics

Computer simulation methods, such as Monte Carlo or Molecular Dynamics, are very powerful computational techniques that provide detailed and essentially exact information on classical many-body problems. With the advent of ab-initio molecular dynamics, where the forces are computed on-the-fly by accurate electronic structure calculations, the scope of either method has been greatly extended. This new approach, which unifies Newton's and Schr\"odinger's equations, allows for complex simulations without relying on any adjustable parameter. This review is intended to outline the basic principles as well as a survey of the field. Beginning with the derivation of Born-Oppenheimer molecular dynamics, the Car-Parrinello method and the recently devised efficient and accurate Car-Parrinello-like approach to Born-Oppenheimer molecular dynamics, which unifies best of both schemes are discussed. The predictive power of this novel second-generation Car-Parrinello approach is demonstrated by a series of applications ranging from liquid metals, to semiconductors and water. This development allows for ab-initio molecular dynamics simulations on much larger length and time scales than previously thought feasible.Comment: 13 pages, 3 figure

Libertà, necessità e legge. Il problema teologico-politico nella polemica tra Hobbes e Bramhall

The controversy against the Anglican Archbishop John Bramhall, in which Thomas Hobbes has been engaged for more than two decades, is one of the most significant steps in the treatment of the theological-political problem by the author of the Leviathan. Focusing on the concept of freedom, on the relationship between will and deliberation, on the relationship between divine omnipotence and free will (and therefore also about the meaning of divine justice and sin), the dispute clearly reveals an intrinsic theological-political character: for both protagonists, this scholastic opposition shows the respective positions in the interpretation of the events of the Civil Wars (1638-1649) and the Interregnum (1649-1660)

La scienza della speranza. Sul marxismo di Ernst Bloch

A prima vista, può apparire strano che un pensatore come Ernst Bloch, che si autodefinisce un marxista, ripercorra a ritroso la strada che dal “socialismo utopistico” ha condotto al “socialismo scientifico”, ed attribuisca un segno positivo alla nozione di utopia. Ma guardando più attentamente a questa apparente regressione, vi si scorgono degli aspetti del tutto nuovi. La nozione blochiana di utopia si costituisce, originariamente, in rapporto con le attese suscitate dalla Rivoluzione d’Ottobre e si inspira, oltre che a profonde radici chialiste, alla teoria e alla prassi del leninismo, alla capacità di Lenin di far maturare possibilità latenti ma non ancora esplicite, di instaurare il socialismo in un paese tradizionalmente ritenuto non idoneo a compiere questo passaggio. La nascita del “marxismo utopistico” coincide paradossalmente in Bloch proprio con la realizzazione del primo Stato socialista, anche se il suo sviluppo è collegato ai limiti storici ed alle contraddizioni che la costruzione del socialismo ha incontrato. Analogamente a quanto Engels afferma dei socialisti utopisti in relazione alla società borghese, si può dire che Bloch avverta le contraddizioni acerbe del socialismo novecentesco senza intravvederne sbocchi immediati, ma rivolgendosi verso un futuro “ulteriore”, alla speranza in un Socialismus absconditus che non ha ancora rivelato il proprio volto