Self Healing Materials
The aim of this Marie Sklodowska-Curie ITN-ETN PhD project is to establish a reliable description of the phase stability, surface and bulk structures and reaction sites for calcite minerals in order to perform studies of the reaction and material transport pathways involved in self healing behaviour.
Initially the phase diagram and equations of state for the bulk calcite phases will be computed: Calcite I, IIIa, IIIb, VI, Aragonite and Vaterite. We will try to obtain a deeper understating of the different phase transformations of calcite structures at high pressures, as they have not been studied deeply. The analysis will start with a high accuracy calculations at the athermal limit using quantum theory based on Density Functional Theory. Then, through the quasi-harmonic approximation, we will calculate the vibrational entropy and therefore take into account the effect of the temperature. This analysis will allow us to calculate the Gibbs free energy, and therefore compare the thermodynamic stability of the phases. If the Gibbs free energy is big enough, we will capture these phases transitions by Molecular Dynamics simulations through a collaboration in this project.
A second line of this project will identify the atomistic structure and pathways involved in the surface chemical reactions contributing to crystal growth. Hybrid and screened exchange functionals in Density Functional Theory will be used in conjunction with local-MP2 perturbation theory to ensure the highest quality energy surfaces currently achievable. The thermodynamics will be computed in the context of the liquid-solid interface.
In a second step, we will study the surface in contact with solution. In a first approximation, the solution will be water and will be modelled initially as an implicit solvent in a continuum approximation. In later studies a few explicit molecular layers will be introduced, as well as the addition of more components to the solution such as organic compounds in order to understand the influence of organic coatings and how organic molecules interact with surfaces in aqueous environments.
The results arising from this study will be compared to AFM-chemical force mapping (Self Assembled Monolayers) experiments performed in Copenhagen University through a collaboration in this project. We will identify those surfaces that involve low activation energy to dissolve into the solution. Using the Nuged Elastic Bond Method we will identify the pathway that makes calcium and carbonate ions to dissolve into the solution. We will explore an hybrid embedding scheme combining the quantum DFT description of interfacial reactions with classical MD simulation of the solution. The final goal will be to make a QM/MM approach using for instance an Electrostatic Embedding (for the Quantum Mechanical part) and a Mechanical Embedding (for the Molecular Mechanics part).
The resulting detailed understanding of the interfacial structure, composition and reaction pathways will be validated again against AFM experiments (University Claude Bernard Lyon) and used to inform the description of the interfacial processes in large scale MD simulations performed by GØran Brekke Svaland and Fernando Bresme.
Link to the project: http://www.nanoheal.uio.no/