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Register a new userStructural Phase Trasformations via Ab-Initio Molecular Dynamics
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Available simulation methods, suitable to describe solid-solid phase transitions occurring upon increasing of presssure and/or temperature, are based on empirical interatomic potentials: this restriction reduces the predictive power, and thus the general usefulness of numeric simulations in this very relevant field. We present a new simulation scheme which allows, for the first time, the simulation of these phenomena with the correct quantum-mechanical description of interatomic forces and internal stress, along with the correct statistical mechanics of ionic degrees of freedom. The method is obtained by efficiently combining the Car-Parrinello method for ab- initio molecular dynamics with the Parrinello Rahman method to account for a variable cell shape. Within this scheme phase trasformations may spontaneously take place during the simulation with variation of external pressure and/or temperature. The validity of the method is demonstrated by simulating the metal-insulator transition in Silicon (from diamond structure to simple hexagonal structure) under high pressure.
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We extend the ab initio molecular dynamics (AIMD) method based on density functional theory to the nonequilibrium situation where an electronic current is present in the electronic system. The dynamics is treated using the semi-classical generalized Langevin equation. We demonstrate how the full anharmonic description of the inter-atomic forces is important in order to understand the current-induced heating and the energy distribution both in frequency and in real space.
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