Reactive MD simulation

  • Chemistry is a study of how molecules interact with each other. One way to understand these interactions is through the study of how energy gets transferred or exchanged between molecules.
  • Chemical processes where the energy transfer between molecules lead to the breaking and/or making of chemical bonds that eventually result in a chemical reaction are called reactive processes.
  • On the other hand, chemical processes that involve transfer or exchange of energy between molecules, but do not necessarily lead to chemical reactions are called nonreactive processes.
  • Chemical dynamics is all about the interplay between energy flowing into these two competing fundamental pathways leading to reactive and/or nonreactive processes.
  • MD simulation is a powerfull tool to show and analysis of reactive and/or nonreactive processes.
  • Reactive molecular dynamics methods refer to a class of MD methods which enable simulation of chemical reactions and chemistry based nanoscale phenomena with accuracy to ab-initio methods. While classical MD provides a powerful tool to simulate nano-scale spatio-temporal phenomena and bulk properties, they lack the ability to simulate chemical reactions. On the other hand, quantum mechanics (QM) based ab-initio methods enable simulations of chemical reactions, but are computationally expensive and limited to a 10’s of atoms. To circumvent this problem, reactive MD methods have been developed which use empirical interatomic potentials with the capability to locally mimic the quantum effects of a bond change due to chemical reactions.

Schematic Representation of the Fundamental Classifications of Chemical Dynamics and the Chemical Processes

  • see bellow figure. Schematic Representation of the Imaginary Time Path Integral Technique. The system in the left side of arrow corresponds to the quantum mechanical system, and the system in the right side of arrow corresponds to the fictitious classical system. The classical system results from the path integral formulation applied to the quantum system and has a partition function that is isomorphic with the quantum system.

Surma Talapatra, Doctor of Philosophy (Chemistry) in The University of Michigan, 2014.

Movie showing the formation of graphitic precursors during reactive MD simulation of pyrolysis process.