"Nuclear Quantum Effects in Molecular Dynamics: A Path Integral Approach and its Relevance to High-Explosives" 

Jalen Macatangay, MSE PhD Candidate 

Advisor: Professor Alejandro Strachan

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ABSTRACT

Molecular dynamics (MD) simulations have advanced understanding of the molecular-scale phenomena that characterize the mechanical, thermal, electrical, and chemical behavior of various materials. However, its approximation that the atomic nuclei behave according to classical physics can considerably undermine the predicted properties. Especially for materials with lightweight atoms and at low temperatures, classical predictions substantially diverge from the true behavior described by quantum mechanics. Yet, calculating the state and time evolution of a quantum system via MD is highly complex and computationally expensive. Over the past decade, methods based on Feynman path integrals have been applied to MD to include nuclear quantum effects explicitly. This approach represents a quantum particle as a classical ring polymer of multiple replicas of the original particle. With this formulation, quantum effects naturally emerge through the simulation of a more complex classical system. This review will highlight the framework of path integral molecular dynamics (PIMD) compared to classical and semi-classical simulation methods. The future potential of PIMD to simulate chemistry under extreme conditions in high-explosives will then be explored based on well-established studies on the water molecule and preliminary simulations at equilibrium conditions.