Questions tagged [phonopy]

Tag this when using the phonopy package for phonon calculations at harmonic and quasi-harmonic levels.

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1answer
52 views

Calculation of linear coefficient of thermal expansion using VASP-Phonopy for Hexagonal material

We use quasi-harmonic approximation using VASP-Phonopy. In whole calculation we only assume Free energy as function of volume but in case of HCP material which have ...
6
votes
0answers
59 views

Phonon Frequencies and Free Energy with respect to polymorphs

I have a material that can crystallize in either a cubic or tetragonal polymorph depending on the synthesis. I used DFPT in VASP and calculated the phonon band structures. I see that the cubic has all ...
7
votes
1answer
72 views

Can we translate vibrational frequencies at q-points to vibrational frequencies of atoms?

Lattice dynamics codes like phonopy output vibrational frequencies at q-points. Can we get data of vibrational frequencies for each of the atoms in the supercell? (...
10
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1answer
73 views

Temperature effect on elastic constant using VASP

I want to incorporate the temperature effect on elastic constant (EC) of a system using VASP. From literature, there are two ways which can be used to get the temperature effect on EC i) ab initio ...
9
votes
1answer
83 views

Reliability about the predicted two-dimensional crystal structures based on DFT high-throughput calculation?

Computational 2D Materials Database (C2DB), 2D structures and layered materials, and 2D Materials Encyclopedia are three major databases for two-dimensional materials based on DFT calculation. However,...
8
votes
1answer
91 views

How to determine LA/TA, ZA/ZO and LO/TO by PHONOPY

I would like to ask how to use PHONOPY to define which band is LO, TO or LA, TA, or ZO or ZA. I attach a picture from https://iopscience.iop.org/article/10.1088/0953-8984/28/10/103005
8
votes
1answer
238 views

Why do we need to build a supercell to use the DFPT in Phonopy interfaced with VASP?

The following passage about the merits of density-functional perturbation theory (DFPT) is extracted from this seminal paper: Phonons and related crystal properties from density-functional ...
9
votes
0answers
152 views

Phonon density of states as a function of frequency vs energy

Lattice dynamics codes like Phonopy output density of states, $g_{(\omega)}$, as a function of frequency. Since $\int g_{(\omega)}d\omega$ is the number of states ...
11
votes
1answer
79 views

Phonon density of states in statistical thermodynamics

Phonon density of states (DoS), $g_{(\omega_i)}$, help understand the distribution of states across frequencies of vibration. $\int g_{(\omega_i)}d\omega_i =$ the number of states between $\omega_i$ ...
15
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1answer
1k views

What do negative phonon frequencies signify?

Negative frequencies "in general" mean the direction of displacement is reverse to that in positive frequencies. Does it mean two frequencies with opposite signs but the same magnitude give ...
4
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1answer
173 views

Best practice(s) for q-points convergence in phonon density of states calculations

The answer can be a complete description of all the things we must be attentive to while converging q-points. A peculiar thing that I feel contradicted about: Generally, we don't take an equal # of k-...
8
votes
1answer
109 views

Should all q-points in the first Brillouin zone be sampled in phonon density of states calculations?

For electronic density of states (DoS) calculations with VASP, it is recommended that VASP's internal symmetry routine is turned ...
9
votes
2answers
120 views

“Input forces are not enough to calculate force constants” Phonopy error?

I am doing a phonon calculation for a phase using a 2x2x1 supercell (after geometry optimization of the structure). I am getting an error when computing the DOS and band structure after computing the ...
25
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3answers
2k views

How big should a supercell be in phonon calculations?

Is 2x2x2 enough, or is larger needed? I know that a convergence test must be carried out, but increasing supercell size enormously increases computational time, and I am using the Python program ...
11
votes
2answers
103 views

Can we do anything to reduce the number of displacements in a frozen phonon lattice dynamics study?

I realize that the more ordered the supercell is, the lower the number of displacements. Perhaps, we could say the same with respect to symmetry. Is there anything that can be done to reduce the ...
19
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1answer
223 views

What do phonon dispersion (or lattice dynamics) studies include?

I use the codes phonopy and phonopy-qha for phonon dispersion studies. phonopy-qha gives ...
16
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1answer
383 views

Are there differences in accuracy and reliability between the frozen phonon method and Density Functional Perturbation Theory?

When proposing or predicting new materials, whether in the bulk or in two dimensions, it is important to discuss the stability of the system. This is usually done through thermodynamics and(or) ...