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The code does not have a function to do that, but it is straight forward to compute the Bose-Einstein occupation function from the temperature and anharmonic phonon frequency. About the sudden change of the vibrational free energy, I guess the SCPH calculation did not converge in the low-temperature region. Did you check if the SCPH loop reached convergence? |
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Hi Terumasa,
It reached convergence but had negative values. PFA the Phonon dispersion graph.
How to improve this? I have changed alpha, convergence threshold and max_iterations in the input file, but the best I could get was this.
Best,
Eesha
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From: Terumasa TADANO ***@***.***>
Sent: Friday, October 14, 2022 9:45 AM
To: ttadano/alamode ***@***.***>
Cc: Eesha Sanjay Andharia ***@***.***>; Author ***@***.***>
Subject: Re: [ttadano/alamode] Extracting Bose-Einstein distribution function for SCPH calculations (Discussion #98)
The code does not have a function to do that, but it is straight forward to compute the Bose-Einstein occupation function from the temperature and anharmonic phonon frequency.
About the sudden change of the vibrational free energy, I guess the SCPH calculation did not converge in the low-temperature region. Did you check if the SCPH loop reached convergence?
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Do you mean you obtained unstable phonon modes even when the SCPH calculation converged? If so, what was |
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Hi Terumasa,
1) Yes, I have obtained unstable phonons in-spite of convergence.
2) I have used the following input paramters:
&scph
SELF_OFFDIAG = 0
MAXITER = 20000
MIXALPHA = 0.01
KMESH_INTERPOLATE = 5 5 1
KMESH_SCPH = 10 10 1
TOL_SCPH = 5.0e-8
/
3. The negative q-point values are shown in the graph. Also, I am unable to include the non-analytical corrections. For this one it does not converge.
Thanks, in advance!
Best,
Eesha
…________________________________
From: Terumasa TADANO ***@***.***>
Sent: Friday, October 14, 2022 9:58 AM
To: ttadano/alamode ***@***.***>
Cc: Eesha Sanjay Andharia ***@***.***>; Author ***@***.***>
Subject: Re: [ttadano/alamode] Extracting Bose-Einstein distribution function for SCPH calculations (Discussion #98)
Do you mean you obtained unstable phonon modes even when the SCPH calculation converged? If so, what was KMESH_INTERPOLATE you used and which q points you found imaginary phonons?
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Where can I find the graph of dispersion curves? |
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This result indicates that the ZA mode frequency near the Gamma point became negative after interpolation even when the SCPH calculation reached convergence at 5x5x1 q points. I think this can happen for 2D systems, where it is often necessary to use a fairly large supercell along the in-plane direction to remove the imaginary frequency pocket around Gamma point even at the harmonic level. I would suggest trying the following:
The imaginary frequency pocket around Gamma may be avoided by using a smaller The above procedure may not solve the issue. If not, I recommend increasing the temperature and computing free energies only above the temperature where the imaginary mode disappears. |
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Hi everyone,
I wanted to know if it is possible to extract and plot the Bose-Einstein distribution function as function of temperature for renormalized anharmonic phonon frequencies using the code?
I want to explain a sudden lowering of MSD value at 300K and in Free energy at around 200K ( Please find attached both the graphs).
Best,
Eesha
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