Faraday Discussions C8FD90031K We have presented the graphical abstract image and text for your article below. This briefly summarises your work, and will be presented with your article online. It will not appear in the print edition. DISCUSSIONS 1 1 Crystal structure evaluation: calculating relative stabilities and other 5 criteria: general discussion Matthew Addicoat, Claire Adjiman, Mihails Arhangelskis, Gregory Beran, David Bowskill, Gerit Brandenburg, Doris Braun, Virginia Burger, Jason Cole, Aurora Cruz-Cabeza, Graeme Day, Volker Deringer, Rui Guo, Alan Hare, Julian Helfferich, Johannes Hoja, Luca Iuzzolino, Samuel Jobbins, 10 Noa Marom, David McKay, John Mitchell, Sharmarke Mohamed, Marcus Neumann, Sten Nilsson Lill, Jonas Nyman, Artem R. Oganov, Pablo Piaggi, Sarah Price, Susan Reutzel-Edens, Ivo Rietveld, Michael Ruggiero, Matthew Ryder, German Sastre, Christian Schon,¨ Christopher Taylor, Alexandre Tkatchenko, Seiji Tsuzuki, Joost van den Ende, Scott Woodley, Grahame Woollam and Qiang Zhu 15 20 Please check this proof carefully. Our staff will not read it in detail after you have returned it. Proof corrections must be returned as a single set of corrections, approved by all co- authors. No further corrections can be made after you have submitted your proof corrections as we will publish your article online as soon as possible after they are received. 25 Please ensure that: The spelling and format of all author names and affiliations are checked carefully. Names will be indexed and cited as shown on the proof, so these must be correct. Any funding bodies have been acknowledged appropriately. All of the editor’s queries are answered. fi 30 Any necessary attachments, such as updated images or ESI les, are provided. 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Oganov 50 Pablo Piaggi DIS C8FD90031K_GRABS 1 Sarah Price Susan Reutzel-Edens Ivo Rietveld 5 Michael Ruggiero Matthew Ryder German Sastre 10 Christian Schon¨ Christopher Taylor Alexandre Tkatchenko Seiji Tsuzuki 15 Joost van den Ende Scott Woodley Grahame Woollam 20 Qiang Zhu 25 30 35 40 45 50 DIS C8FD90031K_GRABS 1 Queries for the attention of the authors Journal: Faraday Discussions 5 Paper: C8FD90031K Title: Crystal structure evaluation: calculating relative stabilities and other criteria: general discussion For your information: You can cite this article before you receive notification of the page numbers by using the following format: (authors), Faraday Discuss., (year), DOI: 10.1039/ 10 C8FD90031K. 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No late corrections can be made. 1 FOR YOUR INFORMATION: You can cite this paper before the page numbers are assigned 25 with: (authors), Faraday Discuss., DOI: 10.1039/ c8fd90031k. 30 35 40 45 50 DIS C8FD90031K_GRABS Faraday Discussions Cite this: DOI: 10.1039/C8FD90031K 211 DISCUSSIONS 1 1 Crystal structure evaluation: calculating relative stabilities and other criteria: general discussion 5 Matthew Addicoat, Claire Adjiman, Mihails Arhangelskis, Gregory Beran, David Bowskill, Gerit Brandenburg, Doris Braun, Virginia Burger, Jason Cole, Aurora Cruz-Cabeza, Graeme Day, Volker Deringer, Rui Guo, Alan Hare, Julian Helfferich, Johannes Hoja, Luca Iuzzolino, 10 Samuel Jobbins, Noa Marom, David McKay, John Mitchell, Sharmarke Mohamed, Marcus Neumann, Sten Nilsson Lill, Jonas Nyman, Artem R. Oganov, Pablo Piaggi, Sarah Price, Susan Reutzel-Edens, Ivo Rietveld, Michael Ruggiero, Matthew Ryder, German Sastre, Christian Schon, Christopher Taylor, 15 ¨ Alexandre Tkatchenko, Seiji Tsuzuki, Joost van den Ende, Scott Woodley, Grahame Woollam and Qiang Zhu 20 DOI: 10.1039/C8FD90031K (200:[200]200) Christian Schon¨ opened the discussion of the paper by Gregory J. O. Beran: Concerning the multi-tier approach to improving the quality of the computations, where you did a careful analysis of different types of approxima- 25 tions, it is still very disconcerting that there appears to be no inherently systematic approach to gain an estimate of the errors involved in the calculations – oen it seems that one does not really know where the error is hiding (e.g. fortuitous error cancellations). This contrasts with the analytical convergence 30 criteria and error bounds one gets when using e.g. perturbation theory, and is quite bothersome (especially since many people do not even try to provide error estimates in the discussion sections of their papers). Do you see any progress in this area? 35 Gregory Beran replied: Quantication of uncertainty is a major challenge in electronic structure theory (and many other areas of chemical simulation). Our preferred, albeit imperfect, approach is to investigate the sensitivity of the prediction to the modeling choices. For example, one can explore how the structures, thermochemical properties, relative polymorph stabilities, or other 40 properties of interest converge with respect to the basis set and level of theory. A few earlier studies from our group exemplify this. For aspirin forms I and II, the relative energy rankings proved quite insensitive to the electronic structure method and basis set, leading to relatively high condence in the relative ener- getics.1 The close similarities in crystal packing between the two forms allow for This journal is © The Royal Society of Chemistry 2018 Faraday Discuss.,2018,211,1–57 | 1 DIS C8FD90031K Faraday Discussions Discussions 1 substantial error cancellation in the relative energies. In contrast, the energy rankings for the ve polymorphs of oxalyl dihydrazide are very sensitive to the electronic structure treatment, making the quantitative stability ranking less certain.2 In that case, the basis set superposition error (BSSE) associated with the 5 intramolecular hydrogen bonding in the alpha polymorph is harder to correct than the BSSE for the purely intermolecular hydrogen bonding found in the other polymorphs. Only in the limit of the large basis sets does one achieve a balanced description of both types of interactions. Perhaps the best example of sensitivity analysis/uncertainty quantication 10 from our work occurs in our recent study, which predicted the methanol phase diagram.3 In that case, by examining how the predicted phase boundaries change upon altering the relative free energies between two forms, we showed that our À calculations reproduced the experimental phase diagram to within 0.5 kJ mol 1. 15 Furthermore, the sensitivity analysis was used to investigate which features of the calculations were most important and where one should focus the computational effort in order to obtain accurate predictions. The Electronic Supplementary Information for ref. 3 goes into considerable detail on these issues. 1 S. Wen and G. J. O. Beran, Cryst. Growth Des., 2012, 12, 2169–2172. 20 2 S. Wen and G. J. O. Beran, J. Chem. Theory Comput., 2012, 8, 2698–2705. 3 C. Cervinka and G. J. O. Beran, Chem. Sci., 2018, 9, 4622–4629. (201:[201]201) Volker Deringer said: You have nicely discussed the different “tiers” of methodology, and how the acetaminophen example was only amenable 25 to the computationally more affordable tiers. How do you expect this to change over time, when more and cheaper CPU time will become available? Do you expect “Tier 1” methods to be routinely in reach within a time frame of a couple of years – and what impact will that have on the eld? 30 Gregory Beran responded: Future advances in computer power will certainly help, but as the timings indicate, the computational cost of a Tier 1 calculation is roughly 200 times that of a Tier 3 or Tier 4 one, and that ratio will continue growing with increasing molecular size. For many applications, the difference between Tier 1 and 3 results may not be worth the difference in computational 35 cost. In the longer term, we think it will likely prove more benecial to move beyond the quasi-harmonic approximation and nd better ways to handle the dynamics and anharmonicity in the crystal, perhaps using machine learning or other approaches to develop accurate potentials that can be sampled more 40 cheaply.