Determination of Ag submonolayer structures on Pt(111) from simulation and data of He scattering experiments

We present a method that adapts the parameters describing the surface dynamics of an epitaxial system to a set of experimental intensities of He scattering at thermal energies. The method is applied to the problem of Ag growth on a Pt(111) surface at temperatures between 250 and 600K

Order and disorder signatures in the specular scattering intensity of He particles from adsorbate covered Pt surfaces

Simulated specular scattering intensity of He particles from Xe and CO adsorbed on Pt surfaces shows distinctive features of the surface order parameters which are, however, not observed in experiments. Inferences may be drawn about the influence of long-range order on the scattering properties. (C) 2000 Published by Elsevier Science B.V

Benchmark calculations of density functionals for organothiol adsorption on gold surfaces

A comparison of density functionals was carried out for systems consisting of a methanethiyl radical adsorbed on gold in different configurations. PW91, PBE, B3LYP and BLYP were tested in a periodic slab approach. Cluster calculations were carried out so as to compare the above mentioned functionals and many others with CR-CCSD (T) and MRMP2 as references. PW91 and PBE provide close results. Energy surfaces calculated by means of PW91, PBE, M06 and TPSSh are in good agreement with the references. M11 performs dissimilarly from M06, in particular it predicts slightly shorter bond lenghts. BLYP gives rather poor results. The semiempirical scheme of Grimme as parameterized in B97-d and the local response dispersion as parameterized in long range corrected BOP-LRD provide very different estimates of the dispersion energy. Unexpectedly rPBE, B3LYP and CAM-B3LYP perform alike and do not match well with the references, though application of a dispersion energy correction in the Grimme scheme, brings them in a much more favorable position

First principle study of processes modifying the conductivity of substoichiometric SnO2 based materials upon adsorption of CO from atmosphere

The electronic structure of tin oxide was studied with ab initio methods with an emphasis on changes induced by adsorption of CO molecules at different surface sites. Purpose of this investigation was to gain a better understanding of the processes underlying the dependence of the conductivity of SnOx based materials on the composition of atmosphere, which is the basis for their usage in gas sensing devices. It was inferred that two different mechanisms could be operating: a mechanism by which CO adsorption modifies the band structure and the order of the electronic levels and another mechanism involving the redox equilibrium between SnOx and CO/CO2 species and the dependence of SnOx, conductivity on oxygen saturation. The present results favour the first mechanism

Stochastic Simulations of Proto-Cells: Lipid Vesicles Dynamics

Stochastic chemical kinetics attempts to describe the time evolution of a well stirred chemically reacting system in a way that takes honest account of the system’s discreteness and stochasticity. In this framework, we have recently developed a computational platform called ENVIRONMENT suitable for designing and testing realistic proto-cell models and possible explanations for their spontaneous emergence in pre-biotic conditions. This software is an improvement of a previous program developed to simulate the stochastic time evolution of homogeneous, fixed-volume, chemically reacting systems that has been modified to be applied to the case of volume-changing, globally heterogeneous, systems. Our aim is to develop models and computational tools to bridge the gap between experimental and theoretical results, focusing the attention on bottom-up and semi-synthetic approaches to construct minimal artificial cells. In this contribution, we dealt with modelling and simulating the structural properties and the experimental dynamic behaviour of lipid vesicle populations used as biomimetic reactors. We start testing our approach by studying fatty acid vesicle dynamics that exhibits some peculiar features with respect to vesicles made of standard lipids as, for instance, the spontaneous formation and faster lipid exchange with the aqueous environment. In this approach, our in silico model of a vesicle in a water solution is composed of three homogeneous molecular domains: the external aqueous phase, the lipid membrane and the aqueous internal core

DFT study of 1,3-benzenedimethanethiol adsorption on Au(111)

A theoretical study of 1,3-benzenedimethanethiol adsorption on Au(111) planar surface at low coverage is conducted. Several configurations were taken into consideration but all of them had both sulphur atoms deprived of the terminal H atom. Also, the case of gold surface reconstruction was examined and results are reported for a configuration analogous to one proposed for methylthiolate adsorption that has lately gained much consensus, one in which both sulphur atoms are coordinated to a single gold adatom