Thesis of Mohammed Hellani

Thesis of Mohammed Hellani - laboratoire UCCS

Abstract :

My thesis work is focused on the simulation of alumina phase transitions. Finding a general collective variable (CV) scheme for such a family of transformations is, in fact, a hard task, but the PathCV-PIV combinations has been proven to be successful. The use of this CV allows tracking transitions among liquid, amorphous and crystalline forms of alumina providing transformation mechanisms and free energy landscapes. We used classical molecular dynamics and enhanced sampling techniques to explore the free energy surface of alumina and characterize the different (meta)stable structures, transformation pathways and energy barriers. In this thesis, we present the application of such an approach to the simulation of the crystallization of amorphous alumina at different temperatures, the connection between stable and meta stable crystalline phases of alumina and the effect of temperature on the free energy landscape of alumina at ambient pressure. The transformations are represented in a two-dimensional space allowing to follow their progress and to identify new phases.

Keywords : Molecular Dynamics,Metadynamics,phase transitions,GROMACS,CP2K,Ab-initio / DFT