[Pw_forum] More on F-D smearing

[Paul Tangney]

Thanks Nicola,

I think that answered my question.
If you're right and what PWSCF calls "total energy"
is E-TS, then "demet" is -TS and is incorrectly
called the "correction for metals" in the code.
As you say, the "correction" should be -TS/2.

If F-D smearing is not a good computational device
then definitely, I agree, the code should call this
"Total Energy" "Free Energy" instead. Otherwise, if F-D
is to be used purely as a smearing technique, the
correct correction should be used...i.e. "demet"
should be changed in the code from -TS to -TS/2.

I'm interested in using F-D in a *physical* way. I want F = E - TS.
So I guess I don't need to change the code at all.

By the way, on the system that I'm studying (crystalline
Tellurium), the application of a finite temperature actually
*lowers* the free energy. Obviously this is unphysical....although
perhaps not totally surprising, given that I'm using a finite
(but dense : 10x10x10) k-point grid. Its still a little worrying though.

Regards,

Paul


-- 
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Dr. Paul Tangney
Theory of Nanostructured Materials Facility
The Molecular Foundry
Lawrence Berkeley National Lab.         E-mail: PTTangney at lbl.gov
1 Cyclotron Road, Bldg 66                  Phone: (510) 642-2635
Berkeley, CA 94720                         Fax :  (510) 643-9345
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