Title: High Mountains and Deep Valleys, Studying Rare Events with Computer Simulations
by Valerio Rizzi (Italian Institute of Technology)

Date: 4 November 2021, 14:00
Place: Physics Seminar Room

Abstract:
Rare events appear in several aspects of life, often in the intersection of scientific disciplines such as physics, chemistry and biology. Relevant phenomena include protein folding, phase transition, ligand binding, chemical reactions and catalysis. The question that we will cover in this seminar is how to exploit computer simulations to better understand them. Computers are routinely used to study matter at the atomistic level with methods such as molecular dynamics. However, the typical timescale that simulations can access is critically limited by the fact that atomic motion unfolds in femtoseconds. Rare events often take place on an immensely longer timescale because the phase space that typical systems explore is very rugged and the systems tend to spend most of the time trapped in deep local minima separated by high free energy barriers. To investigate rare events, we use enhanced sampling techniques that accelerate a system’s dynamics along carefully chosen collective variables and help in crossing the barriers underlying rare events. We will see how these methods allow us to obtain physically meaningful quantities such as kinetic rates and free energy differences between metastable states. We will show a few applications, including chemical reactions, crystallization and the autoionization of water. Further examples can be discussed according to the public’s interests.