Specific Reaction Parameter Multigrid POTFIT (SRP-MGPF): Automatic Generation of Sum-of-Products Form Potential Energy Surfaces for Quantum Dynamical Calculations.

Ramón L Panadés-Barrueta,Emilio Martínez-Núñez,Daniel Peláez

doi:10.3389/fchem.2019.00576

Abstract

We present Specific Reaction Parameter Multigrid POTFIT (SRP-MGPF), an automated methodology for the generation of global potential energy surfaces (PES), molecular properties surfaces, e.g., dipole, polarizabilities, etc. using a single random geometry as input. The SRP-MGPF workflow integrates: (i) a fully automated procedure for the global topographical characterization of a (intermolecular) PES based on the Transition State Search Using Chemical Dynamical Simulations (TSSCDS) family of methods;i (ii) the global optimization of the parameters of a semiempirical Hamiltonian in order to reproduce a given level of electronic structure theory; and (iii) a tensor decomposition algorithm which turns the resulting SRP-PES into sum of products (Tucker) form with the Multigrid POTFIT algorithm. The latter is necessary for quantum dynamical studies within the Multiconfiguration Time-Dependent Hartree (MCTDH) quantum dynamics method. To demonstrate our approach, we have applied our methodology to the cis-trans isomerization reaction in HONO in full dimensionality (6D). The resulting SRP-PES has been validated through the computation of classical on-the-fly dynamical calculations as well as calculations of the lowest vibrational eigenstates of HONO as well as high-energy wavepacket propagations.

Highlights

A detailed knowledge of the topography of a Potential Energy Surface (PES) is a highly desirable prerequisite for the simulation of any dynamical process
We present Specific Reaction Parameter Multigrid POTFIT (SRP-MGPF), a method which provides a well-balanced solution to the aforementioned issues
We present the application of the SRP-MGPF methodology to the actual computation of the HONO (6D) PES for the cis-trans isomerization region, which has become a benchmark for this type of studies (Baranov and Oseledets, 2015; Pradhan and Brown, 2017)

Summary

Introduction

A detailed knowledge of the topography of a Potential Energy Surface (PES) is a highly desirable prerequisite for the simulation of any dynamical process. Owing to our interest in describing chemical processes, we shall turn our attention toward methods able to describe wave packet propagations In this context, within the last few years, we have experienced a boost in dynamical methodologies capable of describing the dynamics of molecular systems up to medium-large size, ranging from semiclassical (Levine et al, 2008; Shalashilin, 2010) to fully quantal (Gatti, 2014). Within the last few years, we have experienced a boost in dynamical methodologies capable of describing the dynamics of molecular systems up to medium-large size, ranging from semiclassical (Levine et al, 2008; Shalashilin, 2010) to fully quantal (Gatti, 2014) With respect to the latter, by far, the most popular approaches nowadays are those based on, or related to, the grid-based Multiconfiguration Time-Dependent Hartree (MCTDH) algorithm (Beck et al, 2000). For the sake of completeness, one should mention the recent and promising direct-dynamics approach of MCTDH by Richings and Habershon (2018)

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Conclusion