Questions tagged [phonons]
Questions related to phonons as applicable to the field of materials science.
78
questions
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32
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DFPT vs analytical nuclear gradient
I have read some literatures about the gradient wrt. atom positions of the DFT energy, and find different methods one commonly used in MD(analytical nuclear gradient,pulay's paper), and another ...
- 31
1
vote
0
answers
26
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Free energy calculation
I want to plot the relationship between free energy and temperature. I want to consider two plots, when phonons are considered and when phonons are not considered how the free energy changes with ...
- 367
4
votes
1
answer
48
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The Appearance of Imaginary Frequencies in Lattice Vibration Calculations with Increasing KPOINTS
I have been conducting lattice vibration calculations using the Density Functional Perturbation Theory (DFPT) method. While investigating the convergence behavior, I noticed that when I increase the ...
- 965
1
vote
0
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50
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Understanding the Interaction Between Phonons and Electrons in Solid-State Systems
How does the wave-particle duality exhibited by electrons and the wave-like nature of phonons enable their interaction in solid-state systems?
Can you explain the underlying mechanisms that allow for ...
- 965
2
votes
0
answers
26
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Non-analytical correction for dielectric constant calculation in VASP
I am calculating the static (low-frequency) dielectric constant for a polar material in VASP.
Due to the LO-TO splitting, I need to apply a non-analytical correction. My question is how to do this ...
- 171
2
votes
0
answers
49
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Comparing phonon dispersions generated with phonopy to those generated with Quantum Espresso
I've generated a phonon dispersion for BCC lithium using the python api for phonopy. I specified the following q-point path
...
- 123
4
votes
1
answer
67
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Why dipole correction does not work in VASP DFPT + phonopy calculation for a stable 2D material
Seems that DFPT method in VASP has many defects. It can't include vdw interaction. Now I found it also can't include dipole correction, which leads to a large negative frequency at $\Gamma$ point. I ...
- 101
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99
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How to get Born effective charge using ph.x for compounds whose constituents are metallic?
In the examples directory of Quantum ESPRESSO PHonon package, example15 shows how to get Raman and Infrared spectra. In the example it contains two compounds ZnO and CO2. In case of CO2, in the ...
2
votes
0
answers
73
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How does Quantum Espresso calculate the dynamical matrices before IFCs in ph.x?
I had a theoretical crisis while I was reading this tutorial.
I know about Density Functional Perturbation Theory(DFPT) and I know that we can approximate the Inter-atomic Force Constants (IFCs) using ...
2
votes
1
answer
104
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Helmholtz vibrational energy from VASP calculations
I would like to calculate the Helmholtz vibrational energy. I have done the phonon calculations. My question is how to extract the vibrational energy from the output of the Vasp calculation.
A source ...
- 367
2
votes
1
answer
75
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Question regarding q2r in QuantumEspresso Phonon Calculation
Let's suppose I've already run an scf calculation for an input file. Now I can read the wave functions and with ph.x I can get the dynamical matrices. I'll get as many files as the number of q-points ...
2
votes
0
answers
32
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Phonon calculations stopped but my computer says it's still running
I have this after typing an htop and all of the CPUs are used but my output file stopped updating 3 hours ago like this:
Should I kill this process? I started this calculation yesterday at 16:00 and ...
2
votes
0
answers
74
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QuantumEspresso phonon calculations stops abruptly with no error
I was trying to calculate phonon dispersion relations of a monolayer MoS2. I've run an Scf calculations with this input file:
...
4
votes
1
answer
183
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How to calculate the Eliashberg spectral function in VASP?
I want to calculate a superconducting critical temperature.
I see in papers like this one: link that they calculate $T_c$ in Quantum Espresso. They use the formula (Eq. 2 in that paper):
$$T_c=\frac{\...
2
votes
0
answers
91
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LO-TO Splitting and Group Theory
I am curious whether or not there is a connection between the group theoretical assignment of phonon modes and LO-TO splitting. For example, is it true that the frequency of a gerade mode will depend ...
- 231
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148
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How to perform carrier doping (hole/electron) for 2D materials by Quantum Espresso? [closed]
I tried to set the tot_charge parameter of Quantum Espresso to alter the charge of the system, but the phonon spectrum I obtained was very strange. Could anyone ...
- 31
5
votes
1
answer
225
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Can you calculate fat ("projected") phonon dispersion bands with Quantum Espresso?
I would like to calculate the fat phonon bands for a chosen material (for simplicity, suppose GaAs), similarily as in Fig. 3 of reference [1]:
This is effectively the analogue of projected band ...
- 283
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votes
1
answer
184
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VASPKIT and SeeK-path recommend different paths. Which one to choose?
I want to get the phonon density of states for a monolayer MoS2. For this, I need phonon dispersion curves, and to choose a path where to compute phonons.
VASPKIT recommends Γ-M-K-Γ
SeeK-path ...
5
votes
1
answer
162
views
project molecular dynamics trajectory onto phonons by normal mode decomposition
After running the Molecular dynamics(MD) simulation, I'd like to see the excitation of phonons during MD, so I'd like to project the trajectory onto a set of phonons, I've seen some paper use the ...
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3
votes
0
answers
61
views
Kohn anomaly and avoided crossing (or anticrossing/level repulsion) [closed]
Kohn Anomaly and Avoided Crossing (Anticrossing/Level Repulsion) are terms that are found to be used when discussing phonon dispersion. The former (see last paragraph, page 198) is related to electron-...
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votes
1
answer
161
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Confusion regarding specifying a k-point path for phonon dispersions/bandstructure plots
I have been trying to obtain a plot of the phonon dispersion of a BCC metal using Quantum Espresso. In the literature it seems that a commonly reported path is ...
- 141
9
votes
1
answer
212
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Zero point correction and free energy calculation with imaginary modes?
I am a beginner in DFT. Recently I have been working on calculating the energy (with zero point correction), and may be free energy in the future, for a structure in both stable and unstable ...
4
votes
0
answers
87
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An issue of running Phonopy for graphene using Siesta [closed]
I have used Siesta in the example attached with phonopy to run phonon for graphene, and when I typed the command to create force ...
- 41
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votes
0
answers
44
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Phonon Angular Momentum
Can anyone help me understand what is Phonon Angular Momentum? How does it affect thermal properties? Any relevant books and papers are welcome, if you have suggestions.
- 1,127
5
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1
answer
141
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Can a material have negative phonon modes in the phonon spectrum but still exist?
I came across a paper which talks about $Cs_2SnI_6$ the material is well researched and there are dozens of experimental papers which say that the material exists in Fm3m space group(FCC), the ...
- 629
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votes
1
answer
518
views
Should one perform geometry optimisation before calculating electronic/phonon band structures via DFT?
I am new to DFT calculations and I would like to get the electronic and phonon band structures of FeSn (1 kagome layer and 1 Sn layer in between). My question is, is it absolutely necessary to first ...
- 121
3
votes
1
answer
182
views
Simple and quick way to get phonon dispersion?
I want a simple phonon dispersion calculation, the lighter the program the better I do not want to install some huge package like QuantumExpresso just for that. Another way would be to find a database ...
- 404
4
votes
0
answers
55
views
q-points weighting factor in QE [closed]
When using Quantum Espresso to perform phonon calculations, one can specify a grid of q-point using ldisp=.true. (Monkhorst-Pack grid)
If I ask for a AxBxC grid, the code will reduce this grid taking ...
- 1,222
7
votes
2
answers
470
views
Details about ZPE and entropy of adsorbates
I want to compute the ZPE and entropic terms for my platinum slab covered by a bilayer of water (network). I have performed a phonon calculation on a 3x3 q-point grid (my unit cell is ~ 4 Å long)
The ...
- 1,222
5
votes
1
answer
197
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k-path for phonon band structure
I have observed in research papers that the k-path chosen for electronic band structure and for phonon band structure to be different. I am currently using VASPKIT in order to obtain the path for ...
- 1,641
9
votes
1
answer
393
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Stability using Phonon Calculation
While performing phonon calculation using finite difference method, we get normal modes printed in the outcar file. Now there is a distinction between two different types of modes in the outcar file.
...
- 111
2
votes
0
answers
78
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How to determine the TA/LA by phonopy [closed]
I would like to ask how to use PHONOPY to define which band is LO, TO or ...
- 21
5
votes
1
answer
85
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Phonon branch-resolved harmonic sampling
I would like to do a phonon band-resolved harmonic sampling, following the recipes from the paper by West and Estreicher (harmonic sampling). In fact, the method presented in the paper is already ...
- 71
10
votes
2
answers
774
views
How to calculate temperature dependent phonon band structure in VASP
I want to calculate phonon band structure using VASP for a double perovskite $\ce{A2BB'X6}$.
Most of the perovskites are well known for dynamical instability at $\pu{0K}$ but show a dynamically stable ...
- 1,663
5
votes
0
answers
55
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How to derive specific heat of a crystalline material from phonon density of states? [closed]
I have done a simulation of a crystalline material using DFT and have extracted its normal modes and its phonon density of states.
Does anyone have an algorithm/code or a detailed resource that can ...
- 1,402
5
votes
0
answers
95
views
How does the VIBRA module of SIESTA compute IR intensities? [closed]
I am working with Fluoro-Graphene (let's assume a fully relaxed monolayer on the XY plane with 16C-1F cell where the F is "covalently" bound to the graphene on top of it with respect to the ...
- 1,402
10
votes
1
answer
1k
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Tools to Visualize Phonons
Software such as ChemCraft or GaussView is easy to find for vibrational calculations in gas phase, but I am finding it much more difficult to find good visualization software for phonons. I have ...
- 10.8k
9
votes
1
answer
214
views
How to improve a phonon spectrum calculation for a monolayer material?
I am a VASP user, and I would like to know what are the things to keep in mind to obtain a good phonons spectrum curve without imaginary frequencies in terms of:
Which method is better for monolayers?...
- 5,683
7
votes
1
answer
858
views
How to solve this Phonopy-related problem?
I have used the finite displacements method for phonon spectrum calculation, and when I typed the command to create force sets:
...
- 5,683
7
votes
1
answer
498
views
Which IBRION tag should be used for finite displacement method in calculating Phonons spectrum?
I am planning to use the finite displacement method for calculating phonon spectrum, and I have prepared the INCAR file below to try it on a transition metal trihalide monolayer (e.g., VI$_3$). I ...
- 5,683
6
votes
1
answer
79
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Which one should be investigated first? dynamic stability or magnetic stability?
I would like to investigate the stability of $\ce{VI_3}$ monolayer, but I am confused about whether I start directly by performing Phonon spectrum calculation, or I should first investigate the ...
- 5,683
6
votes
0
answers
166
views
What is the minimum supercell size for phonon spectrum calculation for this monolayer system? [closed]
Following the previous threads on this topic, I would like to know the minimum supercell size suitable for Phonon spectrum calculation using Phonopy (DFPT) for CrI$_3$ monolayer system given by this ...
- 5,683
10
votes
1
answer
240
views
Can electron-phonon coupling be extracted from the dielectric function?
Computationally, there are various ways to calculate the electron-phonon coupling constants as a function of phonon index and momentum. My question is about the reverse process. Let us say that an ...
- 303
10
votes
1
answer
432
views
Quantum ESPRESSO ph.x output
I wanted to calculate the normal modes of some particular material using the Quantum ESPRESSO. Everything went fairly well, but there is a couple of lines in the output that I do not understand. In ...
- 335
7
votes
1
answer
493
views
Error while installing ShengBTE
I am trying to install the thirdorder script that is mean to work in tandem with ShengBTE on an Ubuntu OS, but I'm getting the following error:
...
- 1,127
5
votes
1
answer
197
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Supercell model for a disordered system in phonon calculations using the harmonic approximation
I studied a disordered state (FCC solid solution) and used a special quasirandom structure supercell with 32 atoms to represent the system. After relaxing it thoroughly with ...
- 5,125
8
votes
1
answer
193
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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 ...
- 1,060
7
votes
1
answer
142
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? (...
- 5,125
7
votes
5
answers
3k
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Quantum harmonic oscillator, zero-point energy, and the quantum number n
The energy of a quantum harmonic oscillator is given as,
\begin{equation}
E_{qho} = \left(n + \frac{1}{2}\right)\hbar\omega,\;\;\;\;\;\; n = 0,1,2,3,... \tag{1}
\end{equation}
I understand the ...
- 5,125
10
votes
1
answer
2k
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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
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