En las fronteras de la Materia Condensada

From the 70's, semi-empirical tight binding hamiltonians have been used widely in solid state physics. If ab initio band structure formalisms as the venerable KKR or APW have been developed before this date, the fantastic increase of the computational facilities has stimulated these last twenty years the development of ab initio electronic structure schemes which are now routinely used. In this talk will be presented few examples where can be seen the interest (and the limits) of non ab initio frameworks. For instance in the case of light adsorbates (as C, N, O) or molecules (as Nh₃ or CO) on transition metal based nanostructures, the semi-empirical tight binding scheme allows to consider complex arrangements of clusters which cannot be yet described by ab initio schemes. In the case of the Magnetic Anisotropy Energy determination of nanostructures, the semi empirical approach leads to a physical understandnis of the subtle oberved behaviours. A major interest in the use of these non ab initio methods is to be able to obtain general trends. In those both cases, will be addressed the answers given today by the ab initio schemes.
 
Acknowledgements: This work has partially benefited of the Research Training Network «Computational Magnetoelectronics» (N° HPRN-CT-2000-00143) of the European Commission.