Phenomene Periodiques

Sommaire Le langage de la théorie des bandes est né dans la physique de l’état solide. Pour les chimistes ce langage est de type exotique. Dans cette leçon nous allons chercher de connecter le langage de bande avec le langage des orbitaux moléculaires, et de voire les états électroniques des solides du point de vue de la symétrie translationnelle

Chemical Computational study of clay minerals and their interaction with pollutants

modelli meccanico molecolari e quantistici delle argill

Modellizzazione su scala regionale della dinamica e della chimica del particolato atmosferico

Nei modelli multiscala di inquinamento atmosferico la descrizione della chimica e della dinamica del particolato atmosferico sono punti assolutamente critici. Particolarmente critico e' il trattamento dell'evoluzione del particolato organico secondario Il progetto include il particolato nel modello fotochimico regional

Maximum Probability Domains in the Solid-State Structures of the Elements: the Diamond Structure

Regions of space are defined to maximize the probability to find two electrons in it. They can be interpreted as regions where Lewis' electron pairs are most likely to be found. These maximum probability domains (MPDs) provide information similar to that obtained from the electron localization function (ELF), but is not identical to it. The elements in the diamond structure provide examples for a comparison

Density-functional Lcao Calculations For Solids - Comparison Between Hartree-fock and Kohn-sham Structural-properties

The Density-Functional method, with Linear Combination of Atomic Orbitals, has been applied to eight crystals: the lattice equilibrium parameters, and the lattice formation energies have been calculated at the Hartree-Fock level (HF), at the hybrid Hartree-Fock Density-Functional level (DFT/HF), and at the Kohn-Sham Density-Functional level (DFT). The band structures and the electronic charge distributions calculated at the DFT and HF levels are compared. (C) 1994 John Wiley and Sons, Inc

Translating Microscopic Molecular Motion into Macroscopic Body Motion: Reversible Self-Reshaping in the Solid State Transition of an Organic Crystal

The amplification of microscopic molecular motions so as to produce a controlled macroscopic body effect is the main challenge in the development of molecular mechanical devices. That amplification requires the coherent and ordered movement of each molecule of a whole macroscopic set, such as that taking place in a single-crystal-to-single-crystal transition. Actually, single-crystal-to-single-crystal transitions in molecular crystals can produce a variety of mechanical effects potentially useful in the development of smart materials. A challenging issue in these dynamic crystals, propedeutic to many possible applications in devices, is the gaining of a strict control over the mechanical effects associated with the transition. Here we report an example in which the control of the mechanical effects was successfully obtained. The compound studied undergoes a reversible single-crystal-to-single-crystal transition at 71 °C, from a planar stacked to a herringbone type packing. To this transition, a reversible macroscopic self-reshaping of the crystal is associated. Depending on the morphology, the crystal specimen undergoes a reversible longitudinal expansion of about 20% or a reversible transverse expansion of 20%, the other two dimensions of the crystal specimen being substantially unchanged. The amount of the macroscopic reshaping effect (20%) fully matches the relative variation of the sole unit cell parameter that changes during the transition (from 8.139 to 9.666 Å) in a sort of scale-invariant process. This represents striking evidence of controlled translation of sub-nanometer molecular motions up to the macroscopic scale of body motion