Multiscale quantum simulation of structure phase change and thermal disruption in nanodot of amorphous carbon

There was a number of experiments, which showed a possibility of phase-change memory building based on amorphous carbon, carried out in IBM Zurich research laboratory.We suggest a multiscale model of phase-change memory. A phase transition is self-consistently simulated on three different time-space levels. On the first level, we use ab initio quantum molecular dynamics calculations with taking into account temperature distribution. On the second level, time dependent evolution of the electronic density is simulated on basis of reduced Ehrenfest molecular dynamics near the line of the phase transition of the second kind. On the third level, we use a heat conduction equation in continuous media to calculate new temperature distribution. For calculations, we used the IBM BlueGene/P supercomputer installed at the Faculty of Computational Mathematics and Cybernetics of the Moscow State University.In this paper we point, that an appearance of a graphitic layer structure from an amorphous state under the influence of temperature effects leads to a localization in space of the electric conductivity. In addition, the temperature profiles, that maintain the structure, become unstable due to the impact of a space-localized heat source. Such a behavior could explain the appearance of s-shaped volt-ampere characteristic in a conducting nanodot during the experiment