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In Quantum Espresso, smearing introduces a temperature that makes calculations converge. A degauss value of 0.1 would mean a temperature of around 1200 K.

Suppose I have the electrical conductivity for a system with a degauss value of (0.1). How can I use it to find the value of that parameter at 0 K or room temperature without running the DFT calculations again?

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    $\begingroup$ Is your system a metal or a semiconductor? Note that smearing only changes the electronic temperature, not the temperature of the ions. In the case of metals, the temperature of the ions have a non-negligible contribution to the conductance, so it has to be modelled explicitly. $\endgroup$
    – wzkchem5
    Jan 12 at 9:16
  • $\begingroup$ Isn't QE input in Rydberg atomic units? If so, 0.1 is nearly 16000 K. $\endgroup$ Jan 16 at 18:19

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The comment by @wzkchem5 is correct - the 1200K equivalent of the 0.1 smearing parameter value has nothing to do with the material's temperature. But you are still right worrying about it. It is a numerical parameter, so you should aim to converge along it. An ideal DFT code would give you the correct result with zero smearing. But in numerical reality it is necessary in case of small or zero band-gaps. So you need to threat it as any numerical parameter, such as basis size or k-grid density, i.e. look for the asymptotic value, estimate variation of your quantity of interest with the smearing magnitude.

Also, smearing to some extent compensates the lack of k-grid density, and vice versa. So you may increase the k-grid density, and check for convergence with smearing 0.2, 0.1, 0.05.

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