Double Proton Transfer in the Dimer of Formic Acid: An Efficient Quantum Mechanical Scheme.

Hao Liu,Jianwei Cao,Wensheng Bian

doi:10.3389/fchem.2019.00676

Abstract

Double proton transfer plays an important role in biology and chemistry, such as with DNA base pairs, proteins and molecular clusters, and direct information about these processes can be obtained from tunneling splittings. Carboxylic acid dimers are prototypes for multiple proton transfer, of which the formic acid dimer is the simplest one. Here, we present efficient quantum dynamics calculations of ground-state and fundamental excitation tunneling splittings in the formic acid dimer and its deuterium isotopologues. These are achieved with a multidimensional scheme developed by us, in which the saddle-point normal coordinates are chosen, the basis functions are customized for the proton transfer process, and the preconditioned inexact spectral transform method is used to solve the resultant eigenvalue problem. Our computational results are in excellent agreement with the most recent experiments (Zhang et al., 2017; Li et al., 2019).

Highlights

Proton transfer plays important roles in various chemical and biological processes (Mayer, 2011; Weinberg et al, 2012; Layfield and Hammes-Schiffer, 2014; Salamone and Bietti, 2015)
The 1D effective potential (EP) for the modes Q6 and Q8 are generated from the full-dimensional potential-energy surface (PES) by minimizing the potential with all the remaining degrees of freedom (DOF), respectively, which is in accordance with the spirit of the process-oriented basis function customization (PBFC) strategy, since the minimum potential is energetically favored in the process of proton transfer
In order to identify important normal coordinates related to the proton transfer of formic acid dimer (FAD) and incorporate them into the current multidimensional research, we first inspect the magnitude of the displacement [| Qi| (i = 1, . . . , 24)] for each normal coordinate from the saddle point to the global minimum

Summary

INTRODUCTION

Proton transfer plays important roles in various chemical and biological processes (Mayer, 2011; Weinberg et al, 2012; Layfield and Hammes-Schiffer, 2014; Salamone and Bietti, 2015). We present efficient QD calculations of groundstate and fundamental excitation tunneling splittings in FAD using the PES of Bowman’s group (Qu and Bowman, 2016), and as for the ground-state tunneling splitting, our calculations yield much better agreement with experiments (Zhang et al, 2017; Li et al, 2019) than previous theoretical calculations. These are achieved with a multidimensional scheme developed by us, in which the saddle-point normal coordinates are chosen and vibrational modes that are strongly coupled to the proton transfer are included. Chemical processes or those desired states by optimizing and adjusting the 1D or nD effective potential (EP)

Normal Mode Hamiltonian

Basis Function Representation

Hamiltonian Martix Solution

RESULTS AND DISCUSSION

SUMMARY

DATA AVAILABILITY STATEMENT