Ab Initio Studies of Size and Coordination Effects：尺寸和协同效应的从头计算研究.ppt

Ab Initio Studies of Size and Coordination Effects Shobhana Narasimhan Jawaharlal Nehru Centre for Advanced Scientific Research Bangalore, India shobhana@jncasr.ac.in First: A Confession Confession (continued) Our group… Reduced Coordination Systems/Phenomena of Interest to Us The Techniques We Use Reconstruction on close-packed metal surfaces Reconstruction on vicinal (stepped) Au(111) Modelling the Reconstruction Scaling Relations Anharmonic Effects Thermal expansion Thermal expansion Conclusions * Kolkata, January 8 2007 Once upon a time… Today… Use ab initio density functional theory (DFT) calculations to explore various aspects of the consequences of reduced co-ordination. + Other applications of DFT to materials problems…. http://www.jncasr.ac.in/~shobhana Lowering of dimensionality usually accompanied by reduction in coordination number. Examples: surfaces, interfaces, nanotubes, nanowires, nanoclusters…. Reduced coordination results in altered structures. Differences in other properties too: vibrational, thermal, electronic, magnetic, chemical reactivity, transport…. dimensionality ? ? C.N. ? Structure (Reconstruction) of surfaces, nanowires, clusters. Elastic properties of these systems (e.g., size dependence of hardness). Vibrational properties of these systems (e.g., surface phonons, etc.). Thermal behaviour (e.g., thermal expansion, melting) of bulk systems, surfaces, nanosystems… Reactivity: dependence on local environment, e.g., rough vs. smooth surfaces, microcrystals vs. nanoclusters. Magnetic properties: especially with reference to how magnetism affects the above. Fairly standard implementations of ab initio density functional theory (plane wave basis, pseudopotentials). Density functional perturbation theory for vibrational and elastic properties. Quasiharmonic approximation / full anharmonicity (from ‘frozen phonons’) for anharmonic thermal properties. Nudged elastic band method for reaction barriers. Parametrized model pot