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\begin{document}
\title{Authors~ response for ``Acceleration of Catalyst Discovery with Easy,
Fast, and Reproducible Computational Alchemy ''~ ~~}
\author[1]{John A. Keith}%
\author[1]{Charles Griego}%
\author[2]{John R. Kitchin}%
\affil[1]{University of Pittsburgh}%
\affil[2]{Carnegie Mellon University (CMU)}%
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\date{\today}
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\href{https://doi.org/10.22541/au.159198180.09946622}{Reviewer 1}'s
original text is given in~\textbf{bold} while our responses are in plain
text.~
\textbf{1. My main question is whether the authors have seen any kind of
finite-size effect on the alchemical potential due to the minimal cell
employed in this study. Due to the coulombic form of the alchemical
potential, it appears unlikely that there is no such effect, but
potentially it is a quite systematic contribution for all target systems
considered.}
While the errors might be attributed as due to finite-size effects, our
group has considered smaller and larger unit cells to describe
adsorbates bound to the surface with different coverages. We find that
first order APDFT is generally more accurate when alchemical derivatives
of or near the transmuted atoms are low, and less accurate when
alchemical derivatives of or near the transmuted atoms are high.~ For
small unit cells with high adsorbate coverages, errors are usually high,
but for large unit cells they are still high if the transmuted atom is
near the binding site of the adsorbate. For now, we prefer to think of
errors in terms of the magnitude of the alchemical derivatives near the
transmuted sites, though considering this as a finite-size effect may
not be incorrect.~~
\par\null
\textbf{2. The authors state ``Computational alchemy is a perturbation
theory approximation''. It might be warranted to rather emphasise in the
article that it is the Taylor series truncation that renders it an
approximation. Under the supposition that the Taylor series converges,
in fact the expansion should be exact. Admittedly, not all of the terms
(e.g. basis function changes in the direction of the alchemical change)
are typically taken into account explicitly, but only if the
perturbation approach is exact in the first place, computational alchemy
can expect to have the predictive power that is required for the
materials design applications outlined in this work.}
This is an excellent point, and we have revised the text here as well as
changed most mentions of ``computational alchemy'' to be ``first order
APDFT'' as the latter is more precise along these terms.~ We have also
changed the text explaining Eq. 4 to better clarify.~ ~
\par\null
\textbf{3. Similarly, when the authors discuss the charge neutrality of
the alchemical change, it might be important to highlight that the
theory does not require the changes in nuclear charges to be strictly
compensated. In this particular application however, the change should
be neutral as otherwise the total surface charge density of the
interface becomes unphysically large.}
We have revised our text to highlight this point.~
\par\null
\textbf{4. When discussing the energy barriers relative to DFT data, the
authors give an error bound of 0.3eV. To set this into perspective: how
accurate can the DFT method expected to be for the systems at hand?
Effectively, computational alchemy constitutes a Taylor expansion on the
potential energy surface of the reference method used, therefore can
only hope to recover the accuracy of the reference method. If this error
bound is low compared to DFT vs higher level methods, this would
effectively render computational alchemy to have predictive power
indistinguishable from the reference method.~~}
This is a good point, but we prefer making a few more qualifying
statements. The text has now been changed to be:
``Even though first order APDFT can exhibit errors as large as 0.3 eV in
barrier heights for reference system doped with just a single atom, it
is promising that such simple approximations can be useful to calculate
a computationally expensive descriptor that guides screening studies.
Furthermore, as the source for errors in different APDFT approximations
become better understood, it becomes reasonable to imagine that more
accurate approaches might be developed based on APDFT that would have a
predictive power comparable (or even indistinguishable) to standard
DFT.''
\par\null
\textbf{5. In Figure 5, the authors show the NEB paths found from
computational alchemy. For the case of Delta Z=-1, NEB image 7 has a
substantially lower energy, even lower than the endpoint of the NEB
path. What is the reason for this given that alchemical predictions are
done on all NEB images in the same fashion?}
We apologize that this was not clear.~ The energies reflect a change in
barrier height with respect to that calculated for the reference
system.~ Thus, we are not reporting a negative barrier, but a barrier
that is lower than the reference calculation.~ Text has been clarified
in the caption.~~
\par\null
\textbf{6. Figure 5 b) is hard to assess visually, since most of the
data points are obscured by others. Perhaps a plot of signed difference
alchemy-DFT vs distance from the transmutation site would be clearer.
Moreoever, no units are given.}
This is a good suggestion, but to be consistent with other data showing
parity plots in this work as well as previous work, we will keep the
data as shown. The main point of the figure is simply to show that this
approach is accurate {when} In future work we will focus more on
elucidating errors and how to correct them, and this suggestion would be
very helpful.~ We now mention the units in the captions .~ ~
\par\null
\textbf{7. In the caption of Figure 2, some cross-references seem to be
mixed up.}
We have corrected these cross references.~~
\par\null
We thank \href{https://doi.org/10.22541/au.159198180.09946622}{Reviewer
1} for reading our manuscript and providing helpful suggestions to
improve our manuscript.~We also thank
\href{https://doi.org/10.22541/au.159198181.14733799}{Reviewer 2} for
making comments within the Authorea document about typos. We believe we
have addressed all points, and we hope that the manuscript can now be
considered suitable for publication in Int. J. Quantum Chem.~~
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