Artículos con la etiqueta ‘Materials Science (cond-mat.mtrl-sci)’

The education of Walter Kohn and the creation of density functional theory

Por • 26 mar, 2014 • Category: Leyes

The theoretical solid-state physicist Walter Kohn was awarded one-half of the 1998 Nobel Prize in Chemistry for his mid-1960’s creation of an approach to the many-particle problem in quantum mechanics called density functional theory (DFT). In its exact form, DFT establishes that the total charge density of any system of electrons and nuclei provides all the information needed for a complete description of that system. This was a breakthrough for the study of atoms, molecules, gases, liquids, and solids. Before DFT, it was thought that only the vastly more complicated many-electron wave function was needed for a complete description of such systems. Today, fifty years after its introduction, DFT (in one of its approximate forms) is the method of choice used by most scientists to calculate the physical properties of materials of all kinds. In this paper, I present a biographical essay of Kohn’s educational experiences and professional career up to and including the creation of DFT.



The Early Years of Condensed Matter Physics at Illinois — in Celebration of the 80th Birth Year of Charles P. Slichter — Charlie Slichter & the gang at Urbana

Por • 15 mar, 2014 • Category: Opinion

The 1950s– and perhaps also the 1960s– were very special times for the development of solid-state/condensed-matter physics. The University of Illinois at Urbana was at the center of these activities. In areas like NMR and superconductivity, methods were developed which would form the basis for the next half century of science and technology. Experimentalists, including Charlie and John Wheatley, worked hand in hand with theorists, including the incomparable John Bardeen. They worked cooperatively to develop ideas, often born in Urbana, but with godparents at Harvard and Moscow and Paris. A characteristic style of broad collaboration and spirited exchange developed and spread from Illinois.



Models and Simulations in Material Science: Two Cases Without Error Bars

Por • 28 nov, 2013 • Category: Educacion

We discuss two research projects in material science in which the results cannot be stated with an estimation of the error: a spectro- scopic ellipsometry study aimed at determining the orientation of DNA molecules on diamond and a scanning tunneling microscopy study of platinum-induced nanowires on germanium. To investigate the reliability of the results, we apply ideas from the philosophy of models in science. Even if the studies had reported an error value, the trustworthiness of the result would not depend on that value alone.



Metallic bonds become molecular-like in atomic-sized devices

Por • 2 jun, 2013 • Category: Educacion

One of the defining characteristics of metals is the way they are held together. Essentially, a lattice of metal ions sits in a sea of delocalised electrons and this acts as a kind of glue that binds the structure together. These “metallic bonds” are entirely different from the covalent bonds that hold molecules together. For a start, metallic bonds are a collective phenomenon that come about because of the bulk behaviour of metal ions and delocalised electrons. But what of the bond that holds together the simplest metal structure imaginable–two metal atoms forming a bridge? Today, Harsh Deep Chopra and pals at The State University of New York at Buffalo say they have characterised the nature of this bond at room temperature for the first time. That could have important implications for the way atomic scale devices are designed and built. “The directional bonds provide high configurational stability to atomic-sized metallic devices,” say Chopra and co.