Questions tagged [phonons]

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

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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
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2 votes
1 answer
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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
87 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
77 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
27 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
1 vote
0 answers
43 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
4 votes
1 answer
64 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
68 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
33 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
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2 votes
0 answers
65 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
78 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
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1 vote
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128 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
100 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
141 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
95 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
37 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
95 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
229 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
102 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
  • 241
3 votes
0 answers
168 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
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5 votes
1 answer
274 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
  • 283
5 votes
1 answer
205 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
188 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
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3 votes
0 answers
66 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
  • 405
6 votes
1 answer
206 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
251 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
97 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
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5 votes
1 answer
155 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
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10 votes
1 answer
549 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
198 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
61 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
  • 1,222
7 votes
2 answers
524 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
  • 1,222
5 votes
1 answer
221 views

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 ...
Parmeet Singh EP 066's user avatar
9 votes
1 answer
426 views

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. ...
mehak g's user avatar
  • 111
2 votes
0 answers
84 views

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 ...
Hu Chenhui's user avatar
5 votes
1 answer
89 views

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 ...
Nikita Rybin's user avatar
10 votes
2 answers
853 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 ...
astha's user avatar
  • 1,663
5 votes
0 answers
55 views

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 ...
Elie H's user avatar
  • 1,392
5 votes
0 answers
104 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 ...
Elie H's user avatar
  • 1,392
10 votes
1 answer
1k views

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 ...
Tristan Maxson's user avatar
9 votes
1 answer
232 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?...
Chi Kou's user avatar
  • 5,713
7 votes
1 answer
926 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: ...
Chi Kou's user avatar
  • 5,713
7 votes
1 answer
527 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 ...
Chi Kou's user avatar
  • 5,713
6 votes
1 answer
83 views

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 ...
Chi Kou's user avatar
  • 5,713
6 votes
0 answers
180 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 ...
Chi Kou's user avatar
  • 5,713
10 votes
1 answer
254 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 ...
KFC's user avatar
  • 303
10 votes
1 answer
464 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 ...
RedGiant's user avatar
  • 335
7 votes
1 answer
538 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: ...
epsilon02fft's user avatar
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