Comment on "Nonlocal statistical field theory of dipolar particles in electrolyte solutions" by Y.A. Budkov

TL;DR

This paper critiques Budkov's nonlocal electrostatics model, highlighting overlooked prior work and emphasizing the importance of comprehensive literature review in scientific research.

Contribution

It provides a critical commentary on existing nonlocal electrostatics models, pointing out gaps and omissions in the literature review.

Findings

Identifies missing references in Budkov's model

Highlights the importance of thorough literature review

Emphasizes originality in scientific contributions

Abstract

The article by Budkov introduces a nonlocal field-theoretic model of solvent-explicit electrostatics. Despite giving a detailed introduction to the early literature on the topic, the article misses out on a series of articles that we published several years ago. Consequently, the manuscript essentially rederives without mention several results that were derived by us for the first time.

Full text

Comment on “Nonlocal statistical field theory of dipolar particles in electrolyte solutions” by Y.A. Budkov

Sahin Buyukdagli1111email: Buyukdagli@fen.bilkent.edu.tr, T. Ala-Nissila2,3222email: Tapio.Ala-Nissila@aalto.fi, and Ralf Blossey4333email: ralf.blossey@univ-lille1.fr

1Department of Physics, Bilkent University, Ankara 06800, Turkey

2Department of Applied Physics and COMP Center of Excellence, Aalto University School of Science, P.O. Box 11000, FI-00076 Aalto, Espoo, Finland

3Departments of Mathematical Sciences and Physics, Loughborough University, Loughborough, Leicestershire LE11 3TU, United Kingdom

4University of Lille, Unité de Glycobiologie Structurale et Fonctionnelle, CNRS UMR8576, 59000 Lille, France

The article budkov18 by Budkov introduces a nonlocal field-theoretic model of solvent-explicit electrostatics. Despite giving a detailed introduction to the early literature on the topic, the article misses out on a series of articles that we published several years ago. Consequently, Ref. budkov18 essentially rederives without mention several results that were derived by us for the first time in Refs. buyuk13-pre ; buyuk13-jcp ; buyuk14-jpcm ; buyuk14-jcp . The work by Budkov also considers variations of our model that are based on a different Yukawa-like solvent structure factor, which enables the exact evaluation of the average electrostatic potential.

In Refs. buyuk13-pre ; buyuk13-jcp ; buyuk14-jpcm ; buyuk14-jcp , we developed the first field-theoretic model of nonlocal electrostatics embodying explicitly the extended charge structure of multipolar solvent molecules and ions with intrinsic polarizability. These articles showed that the consideration of the extended solvent charge structure allows to reproduce the non-local dielectric permittivity fluctuations observed in Molecular Dynamics simulations and solves the problem of the UV-divergence of the free energy without the introduction of an arbitrary cutoff.

In Sec.2.1 of Ref. budkov18 , the Author first derives the nonlocal field theoretic partition function from a formally more general expression by introducing a general solvent structure factor $g(r-r^{\prime})$. Then, this generalization is dropped to switch to the dipolar case. The resulting field theoretic Hamiltonian Eq.(18) becomes exactly identical to the Hamiltonian functionals of our articles buyuk14-jpcm (Eq.(4)) and buyuk14-jcp (Eq.(1)), and the dipolar limit of the more general Hamiltonian of Ref. buyuk13-pre (Eq.(9)). The Author does not cite our previous works in any of these derivations.

The strong overlaps and similarities of Ref. budkov18 with our published work extend beyond Sec.2.1. In Sec.2.2, the dipole limit of the non-local Poisson-Boltzmann (NLPB) equation (22) corresponds to the MF-level NLPB equation of our article buyuk14-jpcm (Eq.(5)) and a restricted case of the more general NLPB equation in Ref. buyuk13-pre (Eq.(12)). Moreover, in Sec.2.3, the linearization of the NLPB equation and its solution in Fourier space (Eqs.(24)-(30)) bears strong similarities to our articles. Most importantly, the dipolar dielectric function in Eq.(31) that follows from this solution is exactly identical to the dielectric permittivity function of Ref. buyuk14-jpcm (Eq.(10)). The latter also corresponds to the restricted case of the more general dielectric function previously derived in Ref. buyuk13-pre (Eq.(21)). Again, no credit is given by the Author to our earlier articles.

The overlaps of Ref. budkov18 with our early works go beyond the MF treatment of the model. In Sec.2.5, the inverse Green’s function in Eq.(56) is similar to Eq.(17) of our article buyuk14-jcp . More precisely, the dipolar limit of Eq.(56) corresponds to the one-loop limit of the (variational) inverse kernel Eq.(17) of Ref. buyuk14-jcp . Finally, in the conclusion part of Ref. budkov18 , the Author expresses his intention to generalize the theory by considering an ”arbitrary electric structure”, via the introduction of ”a probability distribution function of distance for each pair of oppositely charged groups”, without any citation to our non-local field theoretic models of Refs. buyuk13-pre ; buyuk13-jcp where the ionic polarizability was taken into account within a Drude oscillator model.

In summary, we find it disconcerting that the most pertinent references to Ref. budkov18 were not properly acknowledged. This is a severe shortcoming since the Author of Ref. budkov18 knows about our work; he has already referred to our articles buyuk13-pre ; buyuk14-jcp in his publications budkov15 ; budkov16 on point-like dipoles.