[QE-users] oscillations in G(V) diagrams

[Lorenzo Bastonero]

Dear Jakob,

Do you mean the Helmoltz free energy (F)? 

As by definition, the Gibbs free energy (G) does not depend upon volume, but on pressure and temperature.
At p=0, then they are the same, but notice always that:

G(p,T) = min_{V}[F(V, T)+pV] 

Thus, at p=0, you still need to take the minimum of F at the fixed temperature.

Moreover, I guess you are using the quasi-harmonic approximation. There exist several flavours. Unless your system is isotropic, scaling the volume isotropically can be a source of error (due to a physical assumption, not due to the numerics).

Best,
Lorenzo Bastonero

********************************
Lorenzo Bastonero

PhD Student
U Bremen Excellence Chair,
Bremen Center for Computational Materials Science,
and MAPEX Center for Materials and Processes

University of Bremen
Faculty of Production Engineering
TAB-Building, Room 3.32
Am Fallturm 1
28359 Bremen, DE

http://www.hmi.uni-bremen.de/

> Il giorno 4 nov 2022, alle ore 09:20, Jakob Kraus <jakob.kraus at physik.tu-freiberg.de> ha scritto:
> 
> Dear QE users,
> 
> 
> I am trying to calculate heat capacities, and to this end, I have calculated the Gibbs energy as a function of volume
> 
> at several temperatures in a range of 0-700 K.
> 
> However, the functions that result from this do not show a single minimum, but rather a whole lot of oscillations, which
> 
> seem to originate from the phonons, since the E(V) diagram at 0 K shows a single minimum as expected.
> 
> I am thankful for any help you can offer with getting rid of these oscillations.
> 
> I have attached input files and some plots to showcase the problem.
> 
> 
> Best regards,
> 
> 
> Jakob Kraus, TU Freiberg
> <G_Zr_BH4_0.0.png><E_Zr_BH4.png><espresso.qi><espresso.pwi><espresso.phi><espresso.mdi>_______________________________________________
> The Quantum ESPRESSO community stands by the Ukrainian
> people and expresses its concerns about the devastating
> effects that the Russian military offensive has on their
> country and on the free and peaceful scientific, cultural,
> and economic cooperation amongst peoples
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20221105/b9bcdfe7/attachment.html>