Author Topic: Different smearing methods  (Read 12633 times)

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Offline ziand

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Different smearing methods
« on: January 10, 2012, 12:25 »

I know that when dealing with metallic systems, so called smearing is very importend.
ATK uses Fermi-Dirac smearing. Thus an electron temperature is introduced, which softenes the step in the occupation of states at the Fermi level.
The advantage of this method (as I understand) is the fact, that the electron temperature in Fermi-Dirac smearing can be interpreted as the real physical temperature of the system.

However, by looking on other codes and some publications I noticed that there exist other smearing methods. The most prominent are:
- (No smearing (not recommended for metals!))
- Fermi-Dirac
- Gaussian
- Methfessel-Paxton
- Marzari-Vanderbilt
- Tetrahedron method (with Bl├╝gel correction)

Different codes (I looked at siesta, quantum espresso and castep) use different smearing methods as their default. A new siesta-manual praises the Methfessel-Paxton method (can use high electron temp. and low numer of k-points).
Anyway, if you have the time ;-) or don't know what to put in a future release you could consider implementing one or the other of the above methods.

Offline Anders Blom

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Re: Different smearing methods
« Reply #1 on: January 11, 2012, 14:23 »
It's always interesting to hear ideas for features, and we very much appreciate this kind of feedback. We will make a note of your suggestions.

In general, we have more ideas than we have time to implement them, so it's always critical to get an idea for why a particular feature is important, in order to be able to prioritize it properly. Otherwise it becomes a feature just for the sake of the feature, without providing real value.

You have provided a good argument for the Methfessel-Paxton smearing; however, I also note that it can produce negative occupation values (unphysical!) which cause problems e.g. for visualizing the density of states. So, as always, one must tread lightly in these territories :)