[QE-users] Discrepancy in thermal electronic free energy using THERMO_PW

[Elio Physics]

Dear all,

I am trying to calculate the Helmholtz free energy at different temperatures, for the system I am working on, using the THERMO_PW package; however I am getting completely different results using two different calculation schemes:


  1.  Using the  elastic constants calculation, more specifically the ' what='scf_elastic_constants' ' calculation in thermo_control, I get (already converged):

#        T                                energy                           free energy                           entropy                     Cv
  0.10000000E+01  0.252357387447E-03  0.251452023143E-03  0.905364304283E-06  0.269932608244E-05
  0.40000000E+01  0.318043336494E-03  0.217216988656E-03  0.252065869595E-04  0.383593024514E-04
  0.70000000E+01  0.453884623458E-03  0.102158461196E-03  0.502465946088E-04  0.497562746839E-04
  0.10000000E+02  0.609349183616E-03 -0.774788213918E-04  0.686828005008E-04  0.533155503573E-04
.
.
.

  1.  Using 'what=scf_dos' with the by default value of 'deltae', and tricking the code by adding a small degauss value to print out the thermal properties (otherwise it would just print the DOS) , I get completely different results (already converged):

#        T                              energy                     free energy                   entropy                              Cv                      chemical pot
  0.00000000E+00  0.000000000000E+00  0.000000000000E+00  0.000000000000E+00  0.000000000000E+00  0.236129792532-309
  0.10000000E+02 -0.507393714643E+02 -0.507393714856E+02  0.213693218155E-08  0.168706631869E-08 -0.138111664504E+00
  0.20000000E+02 -0.507393714632E+02 -0.507393715059E+02  0.213701188859E-08  0.168699149041E-08 -0.138010404856E+00
  0.30000000E+02 -0.507393714628E+02 -0.507393715269E+02  0.213703845766E-08  0.168696654611E-08 -0.137909145207E+00
  0.40000000E+02 -0.507393714626E+02 -0.507393715481E+02  0.213705174220E-08  0.168695407368E-08 -0.137807885558E+00
  0.50000000E+02 -0.507393714640E+02 -0.507393715709E+02  0.213694949334E-08  0.168705006813E-08 -0.137706592829E+00

So which of these values are to be trusted? I do understand that '2.' is probably for metals  (the system I am working on, is a semiconductor), but  I did not expect this discrepancy in the results.

Any information would be appreciated


Elie Moujaes
Adjunc professor
Federal University of Rondonia
Brazil

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