Questions tagged [dfpt]

Questions related to Density Functional Perturbation Theory.

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The ionic step is not convergent when doing DFPT in VASP

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 ...
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9 votes
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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?...
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6 votes
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What is the minimum supercell size for phonon spectrum calculation for this monolayer system?

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 ...
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6 votes
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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 ...
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8 votes
1 answer
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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 ...
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10 votes
1 answer
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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,...
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9 votes
1 answer
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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 ...
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7 votes
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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 \...
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15 votes
1 answer
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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_{...
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20 votes
1 answer
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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 ...
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18 votes
1 answer
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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) ...
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