Equilibrium Shapes of Ag, Ni, and Ir Nanoparticles under CO Conditions

Round 1

Reviewer 1 Report

In this theoretical study, the authors investigated the equilibrium shapes of Ag, Ni, and Ir nanoparticles under different CO conditions.  Overall, the study was well carried out and was a nice contribution to the literature, however, there exists several major issues that needs to be addressed. [reconsider after major revision]

1.     Title needs to be changed to “…Ag, Ni, and Ir… ”

2.     In Line 41 Ref[15-24] need to be expanded. Especially there are many works using cluster expansions, which is quite suitable for this type of problem:  https://doi.org/10.1021/nl302405k ;  https://doi.org/10.1021/acs.nanolett.6b03867 ; https://doi.org/10.1021/acs.jpcc.8b03868  and https://iopscience.iop.org/article/10.1088/0953-8984/22/24/245401

3.     In Method section, were the k-point density of the (1x1) slab the same as (4x4) slab? Please specify the k-point grid or density.

4.     The PBE functional was used for Ag and RPBE was used for Ni and Ir.  Was it because PBE gives better agreement with experiment for Ag?  Please specify.

5.     Why the authors chose to compute the repulsive energy to be the difference between (1x1) slab and (4x4) slab?  It is coverage-dependent and should be computed at the equilibrium coverage of CO at a given (T,p); the current way of approximation was too crude – the choice of z and w will change everything in equations (4-8) and all the results/conclusion in the paper.  It should be iteratively refined according to the Figures 4-6 (coverage vs. T or p)

6.     Line 92: Ref for F-G isotherm was missing.

7.     Line 135: “don’t” change to “do not” please.

8.     Line 192-194: unnecessary sentence – please remove.

9.     In the Discussion (page 9), please expand it to what are the implications of different shapes/facets and how they can relate to real experiments. Any experimental literatures that can be compared?

10.  Minor issues: In Figure 5: missing label “Ag”; Figure 6: missing label “Ni” and “Ir”; Image resolution needs to be improved.

11.  For all references (page 12) – the journal names were missing. Please check the ref style.

Author Response

We thank the valuable comments of the reviewer very much. Please see the point-by-point response in the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The contribution aims at predicting possible morphological changes of small Ag, Ni, and Ir unsupported nanoparticles depending on CO partial pressure and temperature. Particularly, the authors applied what they refer to as the Multiscale Structure Reconstruction (MSR) model for the calculations. Thus, it was found that the equilibrium shape of Ag nanoparticles is little affected by CO exposure if not at high CO partial pressures for the poor interaction of Ag atoms and CO. In contrast, for Ni and Ir, the shape of the nanocrystals can change dramatically depending on CO pressure and temperature conditions.

The study was well performed, and the conclusions are supported by the calculations. However, the contribution does not bring any element of novelty compared to previous literature reports from the same authors or other groups. Further, the research scope is limited and not realistic. Still, the contribution could be helpful to other researchers in the field. Therefore, I recommend the publication upon minor revision considering the following comments:

1) The submission would improve significantly if the relevance of the contribution were discussed more extensively by referring to realistic scenarios. For instance: Can the authors imagine actual conditions where Ag, Ni, and Ir nanoparticles would be exposed to CO partial pressures compatible with those investigated for the study? 

2) Can the authors describe possible boundary conditions which were considered to simplify the interaction of CO with the different metal surfaces? 

3) In a recent publication (J. Cryst. Growth 2922, 593, 126774), the surface energy CO/Ir phase diagrams were outlined on low-index iridium surfaces. Accordingly, morphological implications of the crystal habit were discussed. How does the present study compare to this recent report?

4) Some details need to be included in Figure 5 and Figure 6 (please compare with Figure 4). In addition, the caption of Figure 6 should be improved to describe all contents better. 

5) Figure 7 could have been better discussed. I suggest describing Figure 7 to a greater extent. What is the relevance of the atomic fraction represented by edges & corners?

6) The bibliography is incomplete. The name of the journal needs to be added to every article.

Author Response

We thank the valuable comments of the reviewer very much. Please see the point-by-point response in the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

3. “The K points of the (4×4) and (1×1) slabs were set as (3×3×1) and (8×8×1), respectively” clearly indicate different k-point densities for these two calculations.  The authors are seriously encouraged to learn more about density functional theory.  Please re-run the calculations with the same k-point density and update all the results (even the changes are small).

5. The publication of the previous work in Angew Chem does not warrant that the method is suitable.  For this paper, please mention the limitation and ways to improve.

Author Response

According to the reviewer's comment, we have performed new calculations and revised the manuscript. The changes can be seen in the attachment.

Author Response File: Author Response.pdf

Round 3

Reviewer 1 Report

1. The choice of 8x8x1 k-point for a (4x4) slab is nonsense and a waste of computational resource.  Have the authors checked k-point convergence? 

What the reviewer meant by "same k-point density" is the following: e.g. if you choose 3x3x1 k-point for (4x4) slab, shouldn't you use 12x12x1 for (1x1) slab?  Or if you choose 8x8x1 for (1x1) slab, then you should use 2x2x1 for (4x4) slab. 

2. When calculating the surface energy, was the slab (1x1)?  What was the k-point for the bulk?  What was the smearing method and width?

 

Author Response

Please see the responses in the attachment.

Author Response File: Author Response.pdf