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Questions tagged [dfpt]

Questions related to Density Functional Perturbation Theory.

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5 votes
1 answer
274 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 ...
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 ...
2 votes
0 answers
133 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?
2 votes
0 answers
99 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 ...
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 ...
15 votes
1 answer
247 views

First order variation of the wave function of conduction states

The first order variation of the wave function $\Delta \psi_n$ is obtained by standard perturbation theory (Eq. 25 of ref 1): \begin{equation} (H_{SCF}-\epsilon_n)|\Delta \psi_n \rangle = -(\Delta V_{...
4 votes
0 answers
140 views

The ionic step is not convergent when doing DFPT in VASP [closed]

I am trying to do DFPT, during the process of moving in different directions, even I set EIDFF=1E-8, the corresponding ionic step is not converged, the relative ...
6 votes
0 answers
181 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 ...
10 votes
1 answer
240 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?...
7 votes
0 answers
114 views

Equations related to the first-order derivative of the wavefunction [closed]

I have two brakets (the angular momentum matrix elements) that are $$ \langle \partial_\mathbf{k} \psi_{n \mathbf{k}} | \times \mathbf{p} | \psi_{m \mathbf{k}} \rangle \tag{1} $$ $$ \langle \psi_{n \...
8 votes
1 answer
229 views

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 ...
6 votes
0 answers
148 views

How can I find primitive axis for any bulk or 2D (monolayer) material [closed]

I am doing DFPT calculations using VASP+Phonopy. To plot phonon band structure, I need a band.conf file in which we need to ...
12 votes
1 answer
194 views

Reliability about the predicted two-dimensional crystal structures based on DFT high-throughput calculation?

Computational 2D Materials Database (C2DB), 2D structures and layered materials, and 2D Materials Encyclopedia are three major databases for two-dimensional materials based on DFT calculation. However,...
11 votes
1 answer
2k views

Why do we need to build a supercell to use the DFPT in Phonopy interfaced with VASP?

The following passage about the merits of density-functional perturbation theory (DFPT) is extracted from this seminal paper: Phonons and related crystal properties from density-functional ...
19 votes
1 answer
3k views

Are there differences in accuracy and reliability between the frozen phonon method and Density Functional Perturbation Theory?

When proposing or predicting new materials, whether in the bulk or in two dimensions, it is important to discuss the stability of the system. This is usually done through thermodynamics and(or) ...
20 votes
1 answer
184 views

What is the importance of electron interaction on dielectric response of crystals?

After obtaining the Kohn-Sham orbitals from a plane-wave-based self-consistent-field calculation, the dipole matrix elements could be calculated in order to determine electro-optical properties such ...