Fisica Computazionale dei materiali mediante dinamica molecolare tight-binding


Discutiamo i principi fisici di base e l'implementazione numerica della dinamica molecolare tight-binding. Presentiamo inoltre una recente implementazione di questo schema di calcolo dove il costo computazionale scala linearmente col numero di atomi presenti nella cella di simulazione. Tale schema risulta naturalmente parallelizzabile ed è stato con successo portato in ambiente CONVEX-EXEMPLAR del CILEA. Concludiamo con una breve rassegna dei problemi fisici attualmente in corso di studio con questa metodologia computazionale nell'ambito delle iniziative promosse e finanziate dal Centro di Modellistica Computazionale. We present and discuss the tight-binding molecular dynamics (TBMD) scheme. The basic idea of TBMD is that the electronic structure of the investigated sample is calculated at any time-step of the simulation by mean of a semi-empirical tight-binding Hamiltonian. Accordingly, the quantum mechanical many-body nature of the interatomic forces is taken into account naturally through the underlying electronic structure via the Hellman-Feynman theorem. The TBMD formalism can be formulated in such a way that its computational workload scales linearly with the number of particles contained in the simulation cell. This formulation is trivially parallelized and runs very efficiently on the CONVEX-EXEMPLAR machine. The TBMD approach is thus able to manage complex systems with directional and covalent chemical bonding, like semiconductor materials, and allows for simulations on a large number of particles (few thousands) for long times (hundreds of picoseconds). These large-scale calculations are at present out of reach of any first-principles approach and therefore TBMD is bridging the gap that exists between cheap (but not accurate) classical simulations and very accurate (but very computer-demanding) ab-initio calculations.



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