Recorded 20 April 2023. Hélène Zapolsky of the Université de Rouen, Haute-Normandie, presents "Atomistic modelling of phase transformation at large time and length scales: atomistic phase field approach" at IPAM's workshop for Scale-Bridging Materials Modeling at Extreme Computational Scales. Abstract: In recent years, significant progress has been made by using molecular dynamic and Monte Carlo modelling to study the physical properties of materials at atomic level. At the same time, recent advances in computational methodologies and massively parallel computers have made it possible to carry out the simulations containing several million of atoms. However, all these advances are not yet well suited to study slowly evolving systems with the typical diffusion time scale. Recently, the new approach, called “Quasi-particles Approach”, based on the Atomic Density Function theory, has been proposed to study the microstructural evolution in different types of materials at diffusion time scale keeping the atomic scale resolution. In this lecture, I will go back to the basics of this approach, introducing the principal equations and main assumptions. Then, I will showcase examples of applications of this method to study the structure of grain boundaries, segregation phenomena at interfaces and displacive fcc/bcc phase transformations. Learn more online at: http://www.ipam.ucla.edu/programs/workshops/workshop-ii-scale-bridging-materials-modeling-at-extreme-computational-scales/