Incorporating Nuclear Quantum Effects into Molecular Dynamics Simulations: A Universe Built on Path Integral Formalism

Farnaz A. Shakib, Ph.D.Assistant Professor, Department of Chemistry and Environmental ScienceNew Jersey Institute of Technology (NJIT)University Heights, Newark, NJ 07102-1982, USA Abstract:Classical molecular dynamics (MD) has been a powerful tool in calculating macroscopic properties of a wide variety of physical, chemical, and biological systems. On the downside, it neglects nuclear quantum effects (NQEs) associated with atomic motions including proton tunneling and zero-point energy. In response, the isomorphism between Feynman’s path integral formulation of quantum mechanics and a classical ring polymer of n beads has been exploited extensively for calculating condensed-phase statistical and dynamical properties subject to NQEs. This led to development of a myriad of adiabatic and non-adiabatic path integral-based methodologies which a diverse range of applicability, accuracy, and efficiency. For efficient MD simulations equipped with a wide selection of state-of-the art path integral formalisms, we have recently introduced DL_POLY Quantum 2.0, a highly parallelized computational suite with a modular structure for incorporating NQEs into large-scale/long-time adiabatic simulations. Furthermore, for non-adiabatic simulations subject to NQEs, we have developed ring polymer surface hopping (RPSH). Here, the non-adiabatic electronic transitions are described through Tully’s fewest-switches surface hopping algorithm while the motion of the nuclei are quantized through the ring polymer Hamiltonian in the extended phase space. We are seeking the practical widespread usage of RPSH with a comprehensive benchmarking of different reaction regimes and conditions with equal emphasis on demonstrating both the cons and the pros of the method. This includes investigating the fundamental questions related to the conservation of energy and detailed balance in the context of RPSH.