Chemical accuracy is $\pu{2E-2 eV}$ but room temperature $\pu{20 ^\circ C}$ is $\pu{2.5E-2 eV}$, so why is it not necessary to take into account thermal effects in DFT? I understood (maybe wrongly) that chemical accuracy is the precision we want on electronic energies for one atom or one molecule.

  • $\begingroup$ $\mathrm{k_B T}$ at room temperature is about $\mathrm{25\ meV}$. $\endgroup$ – Nicolau Saker Neto Sep 9 '20 at 11:52
  • $\begingroup$ Right, sorry ! still it's the same order of magnitude than chemical accuracy... so why it's not necessary to take into account thermal effects in DFT ? $\endgroup$ – Jom Sep 9 '20 at 12:37
  • $\begingroup$ About precission and accuracy, see this $\endgroup$ – Poutnik Sep 9 '20 at 14:26
  • $\begingroup$ DFT can be used to describe electronic structure (and more). It is used nowadays with different functionals, which I like to call density functional approximations (DFA). Most of them have errors beyond chemical accuracy. And there are further approximations, which could handle thermal effects. I'm not quite sure whether I understand the question right, maybe it would be helpful if you could add some more context. In any case: Welcome to Chemistry.se! $\endgroup$ – Martin - マーチン Sep 9 '20 at 14:51
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    $\begingroup$ What is chemical accuracy, and why is it 20meV? $\endgroup$ – Karl Sep 9 '20 at 18:46

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