Affordable Ab Initio Path Integral for Thermodynamic Properties via Molecular Dynamics Simulations Using Semiempirical Reference Potential.

Yuanfei Xue,Ye Mei,Jia-Ning Wang,Yihan Shao,Yan Mo,Jun Zheng,Xiaoliang Pan,Wenxin Hu,Lu Wang,Yongle Li

doi:10.1021/acs.jpca.1c07727

Abstract

Path integral molecular dynamics (PIMD) is becoming a routinely applied method for incorporating the nuclear quantum effect in computer simulations. However, direct PIMD simulations at an ab initio level of theory are formidably expensive. Using the protonated 1,8-bis(dimethylamino)naphthalene molecule as an example, we show in this work that the computational expense for the intramolecular proton transfer between the two nitrogen atoms can be remarkably reduced by implementing the idea of reference-potential methods. The simulation time can be easily extended to a scale of nanoseconds while maintaining the accuracy on an ab initio level of theory for thermodynamic properties. In addition, postprocessing can be carried out in parallel on massive computer nodes. A 545-fold reduction in the total CPU time can be achieved in this way as compared to a direct PIMD simulation at the same ab initio level of theory.

Highlights

For the potential of mean force (PMF) analysis at the density functional theory (DFT) level in the following, we can only trust the results for the region with collective variables (CV) below 0.8 ̊A
The long correlation time of chemical processes in condensed phases plagues the simulations with slow convergence in thermodynamic properties and poses a challenge for the computational studies at ab initio levels of theory
This difficulty is more severe for path integral molecular dynamics (PIMD), in which the representation of quantum effect in singleparticle systems is transformed into a classical problem of discrete cyclic model systems with a number of beads for each atom

Summary

Introduction

Hybrid QM/MM is the method of choice for the studies of enzymatic reactions and chemical reactions in the condensed phase.[1,2,3,4,5,6,7,8,9,10,11,12,13] the application of QM/MM methods is often plagued with extremely poor computational scaling of the ab initio QM methods, as well as the long time scales of molecular dynamics propagation that are usually required before any essential dynamic processes for the degrees-of-freedom (DoF) orthogonal to the boosted one can be observed.[14]. The multistate thermodynamic perturbation (MsTP) is the method of choice, of which the efficiency and reliability has been examined by Li et al in an early study of some model reactions.[45] MsTP is a variant of the reference-potential method, in which the ensemble averages of any time-independent physical properties at a high level of theory are obtained indirectly from simulations at a lower level of theory.

Results

Conclusion