[Thermo_pw-forum] electronic free energy at different temperatures

[Elio Physics]

Dear all,

I am trying to calculate the Helmholtz free energy at different temperatures of a metallic structure (MX2) using the thermo_pw code with  what='scf_dos'.  I am keeping the default value of "deltae" (as instructed)  and using a 10K step for temperature. I am getting the following values: (values are in Ry/cell as given in the output).

 #        T                                 energy                        free energy                         entropy                               Cv            chemical pot
  0.00000000E+00  0.000000000000E+00  0.000000000000E+00  0.000000000000E+00  0.000000000000E+00  0.235589973268-309
  0.10000000E+02 -0.821784411055E+02 -0.821784546975E+02  0.135920658754E-05  0.191338052708E-05  0.585081141513E-01
  0.20000000E+02 -0.821784411050E+02 -0.821784682892E+02  0.135920669618E-05  0.191338051035E-05  0.583642780107E-01
  0.30000000E+02 -0.821784411044E+02 -0.821784818806E+02  0.135920685096E-05  0.191338048653E-05  0.582204418969E-01
  0.40000000E+02 -0.821784411048E+02 -0.821784954731E+02  0.135920675050E-05  0.191338050199E-05  0.580766057297E-01
  0.50000000E+02 -0.821784411051E+02 -0.821785090654E+02  0.135920669024E-05  0.191338051157E-05  0.579327695624E-01

While computing the formation energy according to :
Ef=E(Mx2)- E(M)-2*E(X), where E(M) and E(X) are energies per atom of the isolated bulk M and X species. Adding the above values at different T for MX2 and the individual species M and X (that I have not shown here), gives values of Ef such as -40Ry, which I think are both very large and nonsensical.


  1.  Are the values of the free energy shown above reasonable?
  2.  When inserting the temperature-dependent contributions to the formation energy, does one include the electronic contributions or just the vibrational contributions. Most papers discard the electronic part.

Any help on this topic is highly appreciated.

Obs: I am calculating the temperature-dependent parts because Ef at T=0K for the structure I have turned out to be positive.

Regards

Elie Moujaes
Adjunct professor level III
Federal University of Rondonia
Porto Velho
Brazil





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