Constrained Molecular Dynamic Simulation of the Potential Mean Force of Lithium Bromide Ion Pairs in Acetonitrile

Round 1

Reviewer 1 Report

The manuscript reports the study of molecular dynamics simulations of Li+, and Br- ions in acetonitrile.

The author should address some issues to allow for a fully coherent picture.

1. The author correctly writes, "Understanding ionic association in polar solvents at the molecular level is vital to interpret many chemical and biological processes." Then, he should justify why he chose to study these two ions and their contribution to the scientific community.
2. The material and methods section is well written and detailed. However, there is a total lack of information about the program used to run the simulations.
   The author should provide more details to confirm the accuracy of the software used.
3. The author uses very dated references. In the last 20 years, computational studies have undergone an incredible evolution in terms of computational accuracy. This suggests that the author has not checked recent developments in the technique used, nor has he performed a study of the recent results reported in the scientific literature.
   In fact, he has used models and parameters extracted from papers over 20 years old, which makes me skeptical about the goodness of the results.

The manuscript is well written, and the topic is certainly important, but the author did not address it correctly.

I believe that the contribution could potentially be accepted in Atoms only if the author adds the justifications above.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

In this work, the author conducted constrained and unconstrained MD to investigate the microscopic structure and the conformation of Li and Br ions in acetonitrile. From the former set of simulations, the PMF was obtained.

The topic is interesting, and the simulation work seems to have been done with care. However, I have several concerns that should be addressed. Overall, I consider that the manuscript needs major revision. Below are my comments for the author to consider.

1. The manuscript is not well written. Editing of the English language is required.
2. The author should report details regarding the simulation technique and the statistical ensemble (e.g., NVT or NPT), imposed temperature, and pressure for both types of simulations.
3. In lines 116-117, the author claims that the unconstrained simulations with 215 solvent molecules are in the so-called infinite dilution regime. The author should provide evidence that the corresponding ion concentration lies in the infinite dilution regime?
4. In Figure 2, the results are only flashed, not discussed.
5. In several parts of the manuscript (e.g., line 161, line 175, and line 270), deficiencies are reported regarding comparing the MD results with experimental measurements. The deficiencies are mainly attributed to the united atom model employed for the acetonitrile. Since the simulation cells used in this study are relatively small, the authors could conduct additional simulations using more detailed potentials (e.g., fully atomistic) to see if these deficiencies disappear.
6. The quality of some Figures should be improved. For example, in Figure 2, the author could use a different color for the running coordination numbers. Also, the screenshots in Figure 7 seem too grainy. They should be depicted at a higher resolution.

Author Response

 "Please see the attachment."

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have improved the manuscript, and many critical issues have been resolved. However, I would have appreciated the author updating and expanding the bibliography. Nevertheless, the topic is certainly important, and the manuscript is worthy of publication in Atoms.

Reviewer 2 Report

The author has addressed all points raised. The manuscript is suitable for publication.