Quantum molecular modelling of diffusion process during phase change in amorphous carbon

This paper purpose simulation performing to explain processes taking place in phase-change memory creation. Ab initio quantum simulation of atomic diffusion in amorphous carbon during phase change process is presented. It is shown that thermal effects lead to creation of a graphitic layers structure in a molecular system. Calculations show that in conditions of thermally induced phase change the diffusion process is anisotropic and forced by the fusion of atoms with different bonds and creation of covalent bonds. Time depended process of increasing mean square displacement differs from Einstein relation due to atoms interaction and formation of covalent bonds. Such a structure corresponds to increasing of electric conductivity in comparison with amorphous structure. The density of charge carriers is increased in the area of graphitic surfaces. Obtained dependencies help to understand the mechanism of phase change in experiments directed to the making of phase change memory on the base of amorphous carbon [1].
IBM Blue Gene/P supercomputer installed at the Faculty of Computational Mathematics and Cybernetics of the Moscow State University is used for calculations.