# Questions tagged [dfpt]

Questions related to Density Functional Perturbation Theory.

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### 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 ...
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 ...
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?
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 ...
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 ...
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): (H_{SCF}-\epsilon_n)|\Delta \psi_n \rangle = -(\Delta V_{...
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 ...
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 ...
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?...
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 \...
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 ...
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 ...
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,...
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 ...