Tracking molecular charge distribution along reaction paths with atomic multipole moments

Karol M Langner,Wiktor L Beker,Edyta Dyguda-Kazimierowicz,W Andrzej Sokalski

doi:10.1007/s11224-016-0741-x

Karol M Langner, Wiktor L Beker + Show 2 more

Open Access

https://doi.org/10.1007/s11224-016-0741-x

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Abstract

We explore the idea of supplementing partial atomic charges with cumulative multipole moments for modeling electrostatic effects during chemical reactions. To this end, we investigate the first stage of alkaline hydrolysis of O,O-dimethyl phosphorofluoridate and show how changes in atomic moments provide a more detailed description of charge redistribution during the reaction than is possible using charges alone. Furthermore, the electrostatic potential on the solvent-excluded surface for this reaction roughly converges at the quadrupolar level, with a root-mean-square deviation of ~1 kcal/mol compared to the ab initio Hartree–Fock expectation value. We arrive at similar conclusions for four other reactions, namely the alkaline hydrolysis of demeton-S and phosalone, carbon dioxide hydration, and hydrogen cyanide isomerization. Employing multipole moments on atoms therefore appears to be a feasible and compact way to derive catalytic fields defining the optimal catalytic environment for chemical reactions.

Highlights

An accurate representation of molecular charge distribution is important for modeling chemical reactions, especially catalytic processes which are often dominated by electrostatic effects
We explore the idea of supplementing partial atomic charges with cumulative multipole moments for modeling electrostatic effects during chemical reactions
We investigate the first stage of alkaline hydrolysis of O,O-dimethyl phosphorofluoridate and show how changes in atomic moments provide a more detailed description of charge redistribution during the reaction than is possible using charges alone

Summary

Introduction

An accurate representation of molecular charge distribution is important for modeling chemical reactions, especially catalytic processes which are often dominated by electrostatic effects. Static catalytic fields are defined as molecular electrostatic potential changes during reaction progress [1, 2]. Atomic charges can be calculated from a population analysis of an underlying orbital representation like Mulliken charges [3], or fit to optimally reproduce a physical quantity such as the electrostatic potential [4–6]. One way to improve this it to employ atomic dipoles and higher moments to describe local deviations from an isotropic distribution. This can be implemented as an extension of population analyses using schemes such as distributed multipole analysis (DMA) [8]. We look at the ability of atomic multipole moments obtained using the CAMM scheme to reproduce the molecular electrostatic potentials on the solvent-excluded surface around five reactions involving both neutral and charged reactants. One way to do so is to divide each density element for two basis functions I and J between the two atoms involved: X

NAO X NAO

Findings

Conclusions