Modeling and computer simulation of surfaces and interfaces: development and implementation of a new tool into the Crystal program

Abstract

The recent technological advance is closely linked to the development of new materials, which emerge as an alternative to traditional materials. Lie on the border of research in this new class of materials requires mastery of the most advanced techniques of synthesis, analysis and study of their potential applications in various industrial sectors. The most important properties of materials with relevant technological applications are ruled or even influenced by structural and electronic characteristics of "bulk", surfaces and their interfaces (surface/surface).In particular, the interfaces are the essential point in the improvement of the properties of new materials and which are nearly unknown. The new physical-chemical properties resulting from interfaces or near them are extremely important and can be very different from the expected ones regarding the pure material. As an example, the electronic industry is based on the electrical properties of interfaces of semiconductor-A/semiconductor-B, semiconductor/metals and even sandwich-types like metal/semiconductor/metal or semiconductor-A/semiconductor-B/semiconductor-A, and vice versa. Until now, knowledge and the detailed study, even of the simplest interfaces, still requires deeper theoretical research, which has consequently awaken increasing attention from researchers to understand and elucidate the resulting properties of these new materials. Understanding at an atomic level the morphology and the electronic structure of the interface is a task that can be simplified when analyzed in the light of Theoretical and Computational Chemistry, which has increasingly been used in research and development of new materials. The Theoretical and Computational Chemistry is faced to model structures and properties using the principles of Physics and Solid State Chemistry, helping the development of catalysts, solar cells, capacitors, gas sensors, ferroelectric memories among others. Our research group has devoted part of attention to the simulation of interfaces of oxide/oxides. From the computational point of view this study is not very complicated when the systems involved have the same crystalline phase and similar lattice parameters. A practical example is the interface SnO2/TiO2, where both tetragonal systems are in rutile phase and have very similar lattice parameters. On the other hand, the simulation of systems interface with different crystalline phases, and even structural parameters that differ by more than 10% require a more systematic computational study. The coupling of the different crystalline phases provides a numerical instability and consequently a number of convergence problems. As an example, the simulation of a semiconductor/semiconductor system can often present a metallic character, contradicting experimental results. An example of interface of different crystalline phases is the interface of TiO2 in rutile phase with the hexagonal ZnO. The interface of cerium oxide, CeO2, with zinc sulphide, ZnS is another example of heterogeneous interfaces, which is one of the systems currently studied by our research group. (AU)