Skip to main content

Questions tagged [phonons]

Questions related to phonons as applicable to the field of materials science.

Filter by
Sorted by
Tagged with
1 vote
0 answers
19 views

Never converging phonon calculation in a supercell (Quantum ESPRESSO)

I'm trying to calculate with Quantum ESPRESSO the phonons at the Gamma Point of a Supercell of rutile. I have generated the supercell itself with VESTA and I have tested the convergence for a 2x2x2 k-...
Martino Napoli's user avatar
3 votes
1 answer
19 views

Negative phonon frequencies at finite temperature

I think it is always recommended to perform cell and atom relaxation before starting Phonon calculation. After relaxation the structure represents temperature of 0 K (local minima of potential energy ...
Muhammad Hasan's user avatar
3 votes
1 answer
125 views

Negative phonon calculation

Hi everyone I'm here again to ask you if you know what I can modify to improve my phonon calculation of rutile I think my issues are rooted in not-so-good cell optimizations, I optimize my starting ...
Martino Napoli's user avatar
3 votes
0 answers
66 views

Quantum Espresso - Obtaining Negative Phonon Frequencies

I am new to using Quantum Espresso, I am trying to obtain the phonon dispersion for monolayer InSe. I have previously obtained the band structure with no issues. However, when I move to calculate ...
L_J's user avatar
  • 31
1 vote
0 answers
37 views

Is it necessary to include non-analytical correction in the phonon calculations for intrinsically dipoled monolayers?

Good day, Is it necessary to include non-analytical correction (using Born effective charges and dielectric constants tensors) in the phonon calculations for 2D materials that is intrinsically dipolar ...
UCU110's user avatar
  • 141
5 votes
1 answer
57 views

Phonon calculations related problems

I am performing phonon calculations ph.x of CsPbBr3 primitive cell in QE v7.2 and it is taking a long time on ...
Misbah 's user avatar
  • 333
2 votes
1 answer
54 views

Unit cell size for phonon modes

Based on this and some other literature I realize that the number of phonon modes is contingent upon the size of the unit cell. I also understand that in using Quantum ESPRESSO, the study of defects ...
R Walser's user avatar
  • 367
4 votes
0 answers
46 views

Phonon dispersion calculation of graphene with ASE

I'm trying to use the package ase.phonons to calculate the dispersion relation bands and the DOS, I followed the example of the documentation for Al and went well for the diamond case. For some reason,...
Rob Lut's user avatar
  • 41
3 votes
0 answers
37 views

How to extract the displacement eigenvectors from a phonon calculation?

I'm an undergraduate student using GPAW/ASE for research, and am currently working with the phonon module. I can extract the modes, but aside from using phonopy I can't seem to find a way to get the ...
cinder_shot's user avatar
3 votes
0 answers
41 views

Error in ph.x file

I ran this ph.x file for my structure. However, this response error was displayed. Observation: I made my scf file with norm conserving pseudopotential. The result was ok. Input: ...
Caroline Santos 's user avatar
6 votes
1 answer
124 views

Do the bottom layers of the slab need to be fixed when we use DFPT or finite displacement methods to compute the phonon spectrum of a surface?

When using DFPT or the finite displacement (also known as the frozen phonon) method to compute surface phonon spectra, it is generally necessary to perform high-precision optimization on the slab ...
James's user avatar
  • 65
4 votes
1 answer
77 views

Causes of Straight Bands in Phonon Dispersion Calculations

In my phonon calculation utilizing DFPT in VASP for a monolayer material with space group 187, I've noticed that while most of the phonon bands are positive, two of them appear to be straight. What ...
Farah Shehzadi's user avatar
4 votes
1 answer
152 views

Can we use Density Functional Theory (DFT) to calculate the second and third-order force constants of a slab?

If we aim to compute the surface phonon lifetime of a Cu(111) surface, the second and third-order force constants are essential (to put in Boltzmann transport equation). However, to my knowledge, it ...
James's user avatar
  • 65
4 votes
0 answers
53 views

Comparison of Brillouin Zone Sampling Methods: K-points vs. Q-points

When conducting phonon calculations in VASP using DFPT (Density Functional Perturbation Theory), how do the results obtained using KPOINTS and QPOINTS files compare?
Farah Shehzadi's user avatar
4 votes
1 answer
58 views

Exploring Phonon Dispersion in Two-Dimensional Materials: Analytical Techniques and Mode Identification

How can one analyze the phonon dispersion of 2D materials like graphene to discern specific curves corresponding to particular phonon modes, such as acoustic or optical, as well as longitudinal and ...
Farah Shehzadi's user avatar
4 votes
1 answer
82 views

Thermal vs dynamical stability

Dynamical stability is checked by a phonon curve. Thermal stability is checked by a molecular dynamics simulation. What is the difference between them?
ArduinoEnthusiast's user avatar
4 votes
1 answer
46 views

Simple Quantum Espresso-Phonon

I am completely new to material modelling. I am trying to calculate phonon frequency at X point for Aluminium fcc. I picked an fcc lattice and displaced the atoms at x=0 by (+0.1) and those in x=0.5 ...
PyronGr's user avatar
  • 41
2 votes
1 answer
111 views

Si Thin film phonon dispersion with negative frequency

I have a Si slab of thickness 0.5nm for which I want to calculate the phonon dispersion. The unitcell has 5 atomic layers and 10 Si atoms with vacuum of 10A in z-direction (a 2x2 supercell is shown ...
Mohamed Saleh's user avatar
2 votes
1 answer
90 views

Reproducing ZPE corrections to adsorption from literature

Background In this paper by Lee, et al., they are looking at different functionals and dispersion corrections and how they change the predicted value of CO$_2$ chemisorption on an amine-functionalized ...
Adsorptioneer's user avatar
2 votes
0 answers
115 views

Phonon calculations using Phonopy

Hello everyone: I am doing phonon calculations to plot Helmholtz free energy against temperature. I am using Phonopy with DFPT method. Now I am done but appears if I want to use Phonopy-qha I need the ...
Nana Kofi Boakye's user avatar
4 votes
0 answers
31 views

Incorporating Phonon Calculations as a Criterion for Geometrical Relaxation

In the context of first-principles calculations, such as DFT, lattice vibrations are often determined through phonon calculations, providing valuable insights into the stability and dynamics of ...
Jaafar Mehrez's user avatar
4 votes
1 answer
65 views

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 ...
Fadelis Hu's user avatar
2 votes
0 answers
48 views

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 ...
Nana Kofi Boakye's user avatar
7 votes
1 answer
162 views

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 ...
Jaafar Mehrez's user avatar
1 vote
0 answers
71 views

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 ...
Jaafar Mehrez's user avatar
2 votes
0 answers
43 views

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 ...
random01's user avatar
  • 171
2 votes
0 answers
80 views

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 ...
A quarky name's user avatar
4 votes
1 answer
100 views

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 ...
mollen's user avatar
  • 101
1 vote
0 answers
201 views

How to get Born effective charge using ph.x for compounds whose constituents are metallic? [closed]

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 ...
Niloy Mahanta's user avatar
2 votes
0 answers
199 views

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 ...
CoolerThanACooler's user avatar
2 votes
1 answer
207 views

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 ...
Nana Kofi Boakye's user avatar
2 votes
1 answer
143 views

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 ...
CoolerThanACooler's user avatar
2 votes
0 answers
45 views

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 ...
CoolerThanACooler's user avatar
2 votes
0 answers
117 views

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: ...
CoolerThanACooler's user avatar
4 votes
1 answer
298 views

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{\...
Vladislav Gladkikh's user avatar
2 votes
0 answers
120 views

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 ...
CW279's user avatar
  • 271
3 votes
0 answers
246 views

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 ...
zt liu's user avatar
  • 31
5 votes
1 answer
410 views

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 ...
Neinstein's user avatar
  • 323
5 votes
1 answer
250 views

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 ...
Vladislav Gladkikh's user avatar
5 votes
1 answer
255 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 ...
Jack's user avatar
  • 2,057
3 votes
0 answers
68 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-...
AbPhys's user avatar
  • 811
6 votes
1 answer
257 views

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 ...
aQuarkyName's user avatar
9 votes
1 answer
329 views

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 ...
Hexagon Reversal's user avatar
4 votes
0 answers
113 views

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 ...
Omar Alrawi's user avatar
2 votes
0 answers
48 views

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.
epsilon02fft's user avatar
  • 1,522
5 votes
1 answer
188 views

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 ...
Chan's user avatar
  • 649
11 votes
1 answer
600 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 ...
electronblue's user avatar
3 votes
1 answer
242 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 ...
Jellium mind's user avatar
4 votes
0 answers
67 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 ...
Okano's user avatar
  • 1,417
7 votes
2 answers
626 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 ...
Okano's user avatar
  • 1,417