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I'm a quantum chemist, and nearly every system I've ever cared about has been studied by DFT. However, I am currently trying to model the surface interactions on a nanoparticle around 100 nm in diameter. I know the composition of the nanoparticle, but I do not know which atoms are at the surface versus in the core. It's too large to really be reasonable in my regular DFT packages. Any ideas on where to start?

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    $\begingroup$ For big nanoparticles, you're probably looking at something like ReaxFF. For 100 nm, if this is a million or more atoms, classical MD is not really there. You would need to perform finite element analysis and lose all atomistic information. $\endgroup$ – pentavalentcarbon Apr 18 '18 at 19:16
  • $\begingroup$ Much appreciated @pentavalentcarbon! I think that's what I've been leaning toward and avoiding. Looks like I can't avoid it anymore... $\endgroup$ – AlyChem Apr 18 '18 at 19:21
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    $\begingroup$ I agree with the ReaxFF comment. However, are you sure that you need to model surface interactions on a 100 nm NP? I can't think of many reasons why you'd need to look at a 100 nm surface for a surface interaction (but it's not my work after all!). Why would a periodic cell containing dozens, or even hundreds, of atoms not be sufficient? $\endgroup$ – Argon Apr 19 '18 at 4:47
  • $\begingroup$ @Argon in this case, I am looking at a hetero-nanoparticle and the surface interactions are the second half of a project plan. Initially, I just need to figure out what atoms preferentially appear at the surface. From there, I can simplify my system and look at smaller sections of the surface. $\endgroup$ – AlyChem Apr 25 '18 at 15:45
  • $\begingroup$ @AlyChem Depending on the problem at hand, perhaps you can get away with a smaller cross-section of the NP surface by doing an ab initio thermodynamic approach to predict the most favorable surface structures (e.g. see here diss.fu-berlin.de/diss/servlets/MCRFileNodeServlet/… or check out Chapter 7 of David Sholl's DFT text). $\endgroup$ – Argon Apr 26 '18 at 4:06

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