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Questions tagged [phonon-dispersion]

Questions relating to phonon dispersions - the relationship between the phonon frequency and its wave vector.

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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
0 answers
61 views

Creating a QPOINTS File for Phonon Calculations in VASP

How to construct a QPOINTS file for phonon calculations in VASP, and when is it employed instead of KPOINTS during a VASP standard run for phonon calculations? Could anyone also provide the preferred ...
Farah Shehzadi's user avatar
4 votes
0 answers
43 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
43 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
61 views

Inconsistencies in Phonon Dispersion Results Using Phonopy DFPT with Different Supercell Sizes

I am observing discrepancies in the phonon dispersion results obtained using the Density Functional Perturbation Theory (DFPT) method implemented in Phonopy. Specifically, when I use the same INCAR ...
Farah Shehzadi's user avatar
2 votes
0 answers
134 views

How to create a band.conf File for Phonon Calculations of Graphene with DFPT Method?

How can one generate a band.conf file for performing phonon calculations of graphene with a dim 1x1x1 using the (DFPT) method?
Farah Shehzadi's user avatar
1 vote
0 answers
18 views

Thermal Conductance along the lateral and longitudinal direction

Suppose the left and right leads are both copper rod and the central scattering region is one monolayer graphene sheet. There is no chemical bonding formed between Cu and C atoms. The copper and ...
Kieran's user avatar
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4 votes
1 answer
80 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
5 votes
1 answer
278 views

Phonon calculations using DFPT

I'm currently working on phonon calculations using Phonopy and VASP DFPT approach with a 2x2x1 supercell. I'm seeking guidance on: K-Points Selection: How should I determine the appropriate k-points ...
Farah Shehzadi's user avatar
4 votes
1 answer
40 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
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2 votes
1 answer
90 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
0 answers
31 views

Dynamical Matrix for the Thermal Transmission Coefficient Calculation

The dynamical matrix for the thermal transmission coefficient calculation is written as follows: $$D_{I\alpha,J\beta}(\overrightarrow{q})=\frac{1}{\sqrt{M_{I}M_{J}}}\sum_{b}K_{I\alpha,J\beta}(a,b)e^{i\...
Kieran's user avatar
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4 votes
1 answer
88 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
2 votes
1 answer
123 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
109 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
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5 votes
1 answer
353 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
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5 votes
1 answer
221 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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6 votes
1 answer
255 views

Getting the Phonon Dispersion Using fix phonon in LAMMPS

I am using fix phonon in LAMMPS to get the phonon dispersion relation, but this requires a post-processing code that takes the generated binary file and produces ...
Mohamed's user avatar
  • 695
5 votes
0 answers
282 views

Electron-phonon coupling plotted as function of phonon bands [closed]

I'm looking to superimpose electron phonon coupling (EPC) constants per phonon band per k-point as is done in Figures 6c and 6d in this paper, essentially a "fat band" plot where the ...
user avatar
11 votes
1 answer
586 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
219 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
2 votes
0 answers
42 views

Can we create a phonon with a specific wavenumber that persists in the system for a long time? [closed]

The phonon number is not a conserved quantity, they add up as dictated by the dispersion relation until the Planck distribution is reached. However, I would need the k=PI/a phonons not to disappear ...
user3916292's user avatar
9 votes
1 answer
469 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
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2 votes
0 answers
97 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
2 votes
0 answers
233 views

Phonon dispersion calculation error [closed]

I am getting the following error error in routine phq_readin (1): reading xq I don't understand what is this error about.
epsilon02fft's user avatar
  • 1,522
3 votes
0 answers
102 views

Interpreting Phonon calculations for 2D materials [closed]

What is the meaning of phonon calculation in 2D materials? And is it enough to predict the stability of materials based on positive phonon only?
Maulesh VALA's user avatar
1 vote
0 answers
267 views

can anyone please explain what is meaning of band.conf , mesh.conf and pdos.conf in phonon calculation? [closed]

Can anyone please explain, what is the physical meaning of band.conf, mesh.conf and pdos.conf in phonon calculation? if it is possible please explain about tags used in it.
Maulesh VALA's user avatar
14 votes
1 answer
2k 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
Binh Thien's user avatar
  • 2,095
9 votes
1 answer
141 views

Are there other kinds of stability of materials? How to demonstrate that with computation approaches?

I have known some kinds of stability of materials, such as: Mechanical stability; Dynamical stability; Thermal stability In particular, they can be studied with first-principles computational ...
Jack's user avatar
  • 15.1k
12 votes
1 answer
706 views

Phonon dispersion and phonon DOS

A follow up question for this question. What are the different properties that can be deduced from a phonon dispersion curve and Phonon DOS? Also if possible explain how to deduce them?
Thomas's user avatar
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12 votes
1 answer
252 views

Phonon Calculations for Bilayer 2D systems

I am facing problems in calculating the phonon band structure for bilayer 2D systems. While the band structure mostly shows positive frequencies for the 1 layer system, going to 2 layers makes some ...
Shahid Sattar's user avatar
13 votes
2 answers
368 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 ...
Hitanshu Sachania's user avatar
20 votes
1 answer
655 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 ...
Hitanshu Sachania's user avatar