# Tag Info

### How big should a supercell be in phonon calculations?

Quick Summary: There's no way around performing a convergence test. However, it is possible to obtain convergence much faster than the Phonopy approach by using nondiagonal supercells [1]. The basic ...
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Accepted

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### "Input forces are not enough to calculate force constants" Phonopy error?

This error (input forces are not enough to calculate force constants) may arise when you are trying to plot the band structure or the density of state plots for some systems. Sometimes setting a ...

### Lattice Thermal conductivity calculation error

Partial Answers To remove this error Error in routine cdiaghg (211): S matrix not positive definite Use PAW pseudopotential files instead of USPP. Make sure the exchange correlational functional are ...
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### Calculating lattice thermal conductivity using Quantum ESPRESSO and phonopy

Some years ago I found the following steps in ResearchGate: You need: QuantumEspresso (QE) Phono3py ShengBTE & thirdorder.py First, you need to create a QE input file (...
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### Can we translate vibrational frequencies at q-points to vibrational frequencies of atoms?

As known [1], the eigenvalues of the dynamical Hessian matrix represent the phonon frequencies, whereas the eigenvectors represent the particular atomic displacement patterns contributing to the ...

### Phonon frequencies and free energy with respect to polymorphs

Your interpretation of the results. I agree with you that if you find no imaginary frequencies in the cubic phase it means it is at a local minimum of the potential energy landscape, and that if you ...
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### Temperature effect on elastic constant using VASP

The following paper is quite nice, in my opinion: Shang et al., Temperature-dependent elastic stiffness constants of α- and θ-Al2O3 from first-principles calculations, J. Phys. Condens. Matter 22 (...
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1 vote

### How to calculate the lattice parameter of a supercell using Phonopy? (For Quantum ESPRESSO)

The process you described for obtaining a supercell can be found here. If the 1*1*1 unit cell has a lattice parameter of a, then a 2*2*2 supercell will have a lattice parameter of 2a, a 3*3*3 ...
1 vote

### k-path for phonon band structure

The question was: "but why do some articles use different path" However, no article was provided that uses a different path. ProfM said: "I agree there is no reason why the two paths ...
1 vote

### Phonon branch-resolved harmonic sampling

OP: "Hello! Perhaps, the most general formalism, which would allow to perform such analysis is based on the Berry phase theory. There are a bunch of papers doing this, for example, journals.aps....

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