[Pw_forum] Mermin free energy & Fermi-Dirac smearing

[Paul Tangney]

Hello,

I am trying to calculate the total (free) energy of
a semiconductor with electrons at a high temperature.
I am doing this by tinkering with the Fermi-Dirac smearing
scheme in PWSCF. Now, as far as I know, if F-D smearing is
used purely as a computational device for metals, the
ground state energy should be calculated (estimated) by
E_0 = E - TS/2 , where E is the standard Kohn-Sham energy
and the second term is half the electronic entropy energy.
Is this correct ?

What I want is to calculate F = E - TS, the free energy.
However, when I looked in the code (subroutines "gweights" and
"w1gauss" ) it appears to me that the ground state energy
for metals is being calculated as E_0 = E - TS.
In other words, the correction term is twice what it should
be. Am I right about this, or am I reading the code wrong ?
Factors of two can have many origins.
Is the variable "demet"  TS or TS/2  ?

If I can figure this out, I can figure out how to get
the quantity I want.

Thanks for any help,


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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