\textit{This manuscript reports a major advance in electronic structure theory, by providing a cheap and mathematically motivated correction for finite basis size effects in high-level theories.
I expect it to have immediate applications among users, certainly once user friendly code is released.
The work is definitely worthy of being published in JPCL, after changes.
That said, for the reasons explained below, I think the current manuscript requires changes somewhere between major and minor.}
We strongly believe that adding more technical details would not improve the readability of the present paper, especially for the wide audience of a journal like JPCL.
In the present manuscript, we point out clearly the key equations of Ref.~[41] and we refer the reader to this reference for further details.
Note that this is the only point where we disagree with the reviewer.}
\textit{This readability issue is not made easier by the authors' commendable focus on generality, which leaves the reader carrying a lot of variables and ideas in their head.
My first suggestion to the authors would be to change from describing things in terms of a generic method "Y" to using a specific case [e.g. CCSD(T)] and then generalizing only at the end, e.g., "Of course, the above holds true for any method that provides a good approximation to the energy, not just CCSD(T).".
\textit{What I think would be very useful is to show $\mu(\bm{r})$ for an example, e.g. along the bond in an interesting diatom.
This would illustrate the range of values taken by $\mu$, and the advantage of doing things point-by-point.
If values for multiple basis sets were reported it might also help in understanding how and where larger basis sets help, which might point to how to improve basis sets in a more systematic fashion.
Removing the discussion on LDA would probably free enough space to show this, especially if Figure 2 was condensed into a single figure (which should be feasible sans LDA).}
\textit{One final (minor) key point is that the proposed use of density fitting or related time-saving steps seems rather ambitious, given that it necessarily introduces a further basis set dependence.
I would suggest the authors do not mention the last sentence in the relevant paragraph, or give more detail if it is included.}
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\alert{Following the reviewer's advice, we have removed our comment on density-fitting and related methods.}
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\textit{Regardless of my issues with presentation, this is important work which should definitely be published in JPCL.
It just first needs to be made a bit easier to follow.}
\noindent\textbf{\large Authors' answer to Reviewer \#2}
\textit{This is an excellent paper on density-based basis-set corrections for accelerating the basis-set convergence of an arbitrary wavefunction method.
The corrections are examined for the atomization and correlation energies of the G2 set of molecules.
In wavefunction theory, F12 methods have been developed in the 2000s.
The approach described in this paper provides a fast alternative to F12 that requires relatively large auxiliary basis functions for computing three- and four-electron integrals.
As a small notice, I suggest the the following for an update of reviews on F12, Grueneis et al., J. Chem. Phys., 146, 080901 (2017), Ma and Werner, WIREs Comput. Mol. Sci., 8:e1371 (2018).
To summarize, I think this is an excellent paper that should be published in JPCL basically in the present form.}