26
votes
Accepted
What do negative phonon frequencies signify?
Phonons are a measure of the curvature of the potential energy surface about a stationary point. In particular, the matrix of force constants is calculated as:
$$
D_{i\alpha,i^{\prime}\alpha^{\prime}}(...
- 11.2k
12
votes
Accepted
Phonon dispersion and phonon DOS
The phonon dispersion relates the phonon frequencies $\omega_{\mathbf{q}\nu}$ for each branch $\nu$ with the phonon wave vector $\mathbf{q}$, typically along a path in the Brillouin zone joining high-...
- 11.2k
6
votes
Accepted
VASPKIT and SeeK-path recommend different paths. Which one to choose?
If you check out this picture of the Brillouin zone of a hexagonal cell, you can see points like L, A and H are defined for a 3D Brillouin zone. This is because the k-path finding algorithms are ...
- 1,336
6
votes
Obtaining phonon density of states from Density Functional Theory
Short answer. Yes, it is possible to calculate the phonon density of states using density functional theory. You can calculate the phonon frequencies on an arbitrarily large $\mathbf{q}$-point grid to ...
- 11.2k
5
votes
Phonon density of states in statistical thermodynamics
There are two possible things tripping you up here:
Phonons are collective oscillations: they involve the motion of all the atoms together. Therefore it only makes sense to talk about the phonons of ...
- 6,794
4
votes
Should all q-points in the first Brillouin zone be sampled in phonon density of states calculations?
Background. The phonon density of states $g$ is given by:
$$
\tag{1}
g(\omega)=\sum_{\nu}\int\frac{d\mathbf{q}}{(2\pi)^3}\delta(\omega-\omega_{\mathbf{q}\nu})\approx\frac{1}{N_{\mathbf{q}}}\sum_{\nu}\...
- 11.2k
4
votes
Causes of Straight Bands in Phonon Dispersion Calculations
Such bands are usually called 'flat bands'. The group velocity vanishes, signalling that such an excitation is non-dispersive, i.e. is localized. See here. Think 'molecular modes'. For an isolated ...
- 1,668
3
votes
Exploring Phonon Dispersion in Two-Dimensional Materials: Analytical Techniques and Mode Identification
Do you know what longitudinal, transverse, acoustic, and optical mean in this context? Or you want a code that can tell you what they are?
If you know what they mean, you can plot the displacements ...
- 1,668
3
votes
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 ...
- 346
3
votes
Accepted
Quantum ESPRESSO 7.0: Why ph.x does not produce .dyn files?
From your input files, everything is good. But you have to attach also phonon calculation output file. At lease you have to write last line of phonon calculation output file. From given informations, ...
- 91
2
votes
Negative phonon frequencies at finite temperature
If you perform an atom relaxation before the phonon, you also get a 0 K result wrt. atom positions. You will need to perform an MD simulation to simulate effects from temperature properly.
I would ...
- 11.4k
2
votes
project molecular dynamics trajectory onto phonons by normal mode decomposition
DynaPhoPhy
DynaPhoPhy is an open source (MIT License) python library for Phonon anharmonic properties from Molecular Dynamics.
DynaPhoPhy allows to calculate anharmonic phonon linewidhts and
...
- 3,145
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