Questions tagged [density-functional-theory]

For questions about simulations using Density Functional Theory.

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5
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Which specific perturbation do we consider applying to the potential when defining the energy derivative of the log derivative?

Norm-conserving pseudopotentials are defined such that the energy derivative of the log derivative of the real and pseudo wavefunctions agree at $r>r_c$. I understand that although valence ...
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47 views

How to identify/treat delocalized pi bonds in DFT

For a structure such benzene, the pi bonds between the carbon atoms are said to be de-localized. Therefore the electrons are expected to be exchanged in between individual C-C bonds. When dealing with ...
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1answer
43 views

How to understand the energy derivative of the logarithmic derivative of a wavefunction when deriving norm-conserving pseudopotentials

The 4th desirable property of a norm-conserving pseudopotential given by Hamann et al is for the 'logarithmic derivatives of the real and pseudo wave function and their first energy derivatives agree ...
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80 views

Physical interpretation of k-points

What is the Physical interpretation of the k-points used in ab initio calculations? Why must the number of k-points be optimized rather than just using some large fixed number of them?
6
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1answer
110 views

How does electronic iteration work in a VASP relaxation calculation?

I am a beginner using VASP to do material modeling, and I'm confused about the following questions: How does the electronic iteration work in VASP relaxation calculation? Is the electronic iteration ...
8
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1answer
264 views

Study of supercell after creating vacuum

For studying a bulk supercell, after creating some vacuum in it, I'm confused about how to relax it. With VASP, I can do relaxation using NSW = 0 and ...
6
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2answers
80 views

Relation between lattice parameter and energy for relaxations

We have been wanting to do relaxation of lattice parameters as a function of the energy. I want to know the mathematical expression for this, and also the theoretical background related to this method....
8
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1answer
76 views

what do I need to change about typical VASP input file to calculate the energy of a single atom?

I'm a little confused how to make a VASP input file to calculate the energy for the isolated atom: Do I need to change the lattice parameter of my unit cell or can keep the value for the whole system?...
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20 views

TIP5P model for water in RISM

I want to use the implementation of ESM-RISM from the Otani laboratory using Quantum Espresso. For my system I ask for $H_2O \; (H^+Cl^- \; 1M \; aq.)$, following the literature the best way to ...
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33 views

Cutoff length for vdW correction in DFT calculation

In classical MD simulations of lattice structures, whenever we are trying to incorporate vdW corrections to the atomic force calculation, we need to set up cutoff length beyond which the vdW ...
9
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1answer
65 views

How to confirm whether a system is mott-insulator or not from DFT calculations?

I am using Quantum-Espresso and I need to study mott-insulator. Being a beginner, I am not sure, how do I confirm whether my system is a mott-insulator or not?
7
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1answer
95 views

Lattice Thermal conductivity calculation error

I have been trying to calculate Lattice Thermal Conductivity on my system using QuantumEspresso. I used phonopy and phono3py. I was successful to run these codes on Si system for practice. Now when I ...
5
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1answer
31 views

How to fix local magnetic moment of each ions in VASP?

In spin-polarized calculation,total magnetic moment can be fixed to a specific value using NUPDOWN tag. In non-colinear spin calculation, tag ...
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What are the challenges in using DFT to study the Hydrogen Evolution Reaction of (111), (110), (100) and (011) planes of Cobalt (III) Phosphide (CoP)

What are the challenges in using DFT (implemented in the VASP code) to study the hydrogen evolution reaction (HER) of the (111), (110), (100) and (011) surface planes of Cobalt (III) Phosphide CoP
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26 views

Case study: KPOINT and band parallelization in Quantum ESPRESSO

I am testing Quantum ESPRESSO with different values for Npool and bands in order to calculate run time. ...
8
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1answer
443 views

Kramer's Degeneracy and Antiferromagnetism

How can one understand the concept of Kramer's Degeneracy for an antiferromagnetic system where spin-up and spin-down bands overlap due to net zero magnetic moment?
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1answer
62 views

How can I build an MoS2 nanoribbon?

Are there any codes available? What is the easiest way?
5
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1answer
48 views

How do I relax only the in-plane component of the unit cell?

I know that &CONTROL='vc-relax' option calculation performs a unit cell relaxation, and that the ATOMIC_POSITIONS can be ...
5
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2answers
63 views

SIESTA output wavefunctions: all vs selected?

Using SIESTA, I want to plot the wavefunctions around the Fermi level (similar to HOMO/LUMO). Also, I want to do COOP analysis. From the SIESTA manual, I can setup to write the wavefunctions ...
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48 views

Job stops in between without showing any error

I am trying to calculate the dos of one bulk system. My dos calculation job stops in between without showing any error. Here I am attaching the link of my input dos calculation files. CONTCAR file is ...
7
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1answer
85 views

Different band gap observed in unitcell and in the supercell

I calculated the bandgap for one system in the unit cell and in the supercell of 2x2x1 and 3x1x1. Although 3x1x1 gives the same bandgap as I got from the unit cell (1.79 eV) but 2x2x1 is giving 1.75 ...
6
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1answer
91 views

How to evaluate the electron relaxation time of nanostructures computationally

I am working with Si nanowires using the SIESTA ab initio code and the BoltzTraP2 Boltzmann transport equation solver. However, the output of the BoltzTraP2 code comes per relaxation time (...
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40 views

Comments on the electronic relaxation time variation between nanowire configurations

I am studying Si nanowires with different cross sections. In my work, I plan to evaluate the thermoelectric performance variation between different configurations. To achieve this, my current approach ...
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72 views

How to implement a toy DFT [duplicate]

I want to learn DFT for research purposes and I need to implement a toy DFT for pedagogical reasons. I would like some recommendations regarding resources like books, articles, or any other thing that ...
10
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1answer
56 views

How to identify localized surface states in the band structure

After calculating the band diagram of a structure, is there a way to identify localized surface states? I am working with Si nanowires with different cross sections. I want to determine the band gap ...
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68 views

Why am I getting DOS like this in Quantum ESPRESSO?

I am working on $\ce{GeHfTe}$ and in the case of a non-collinear calculation, I am getting the DOS in the attached photo. I have already relaxed my structure with VC-relax and it is converged with ...
10
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2answers
83 views

Doubt about K point selection for 2x2x1 supercell

I have one doubt about K points selection for a supercell. I construct one 2X2X1 supercell with 64 atoms having a=11.19, b=11.19, c=5.59. For checking K points convergence test with energy should I ...
7
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1answer
65 views

Eigen-values not converged, warning in Quantum espresso

I am running a simple example of vc-relax/scf for aluminum using PBE pseudo-potential.Setting are given below ...
7
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1answer
67 views

How to perform linear response theory calculation of U Hubbard parameter in VASP?

Following to this post, I would like to know how to perform linear response theory for calculation of U Hubbard parameter in VASP?
10
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2answers
191 views

Non-Convergence of the XC functional in the sense of a Taylor series

When it comes to improving the accuracy of DFT calculations, there is a well known hierarchy: starting from LDA using $E_{xc}[n]$, proceeding with GGA and its $E_{xc}[ n, \nabla n]$ dependency and ...
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76 views

Calculate FF interaction energy of small molecular dimers

I have a set of molecular dimers (~25 atoms) for which DFT-D3 interaction energies are calculated by Psi4 and Turbomole program. Now I want to compare these values against Force-Field methods like UFF/...
10
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1answer
278 views

Accuracy trade-off between energy and density in DFT calculations

Consider the following situation that the exchange-correlation term (e.g., B3LYP) overestimates the energy in a system (i.e., a simpler one (e.g., LDA) is sufficient in the system). In this case, my ...
5
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1answer
44 views

Tool to saturate the dangling bonds at the surface of nanostructures

When it comes to studying 2D, 1D or 0D nanomaterials, saturating the dangling bonds in the surface helps remove unwanted localized surface states from the band structure 1. However, so far I have not ...
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36 views

Smearing values for different codes

I am using Quantum Espresso along with a different code, I am performing calculations on Platinum bulk. After choosing the "cold" smearing (which I read is a good choice for metals) with a ...
8
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1answer
113 views

Geometry optimization using DFT

I have been attempting to optimize the structure of a Si nanowire using SIESTA. The original structure fed into the optimization is as follows. Once it is optimized, the structure would change to ...
9
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1answer
97 views

Error in nscf calculation while considering Spin Orbit Coupling in Quantum ESPRESSO

I am trying to do the band structure calculation considering the Spin Orbit Coupling but getting the following error: ...
7
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1answer
49 views

Effective mass convergence

What's the point of using extremely denser k-grid for extracting curvature effective masses? I saw in some publications that they use extremely dense k-grid for band structure calculations for ...
5
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1answer
86 views

How to calculate the Berry connection difference?

For Bloch electrons, the Berry connection is defined as $$ \mathcal{A}_n(\mathbf{k}) = i\langle u_{n\mathbf{k}}|\partial_\mathbf{k}|u_{n\mathbf{k}}\rangle \tag{1} $$ where $u_{n\mathbf{k}}$ is the ...
7
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1answer
129 views

How to generate a input file for gaussian in Avogadro 2? [duplicate]

I made auto optimization working by installing openbabel using sudo apt install openbabel. Is there any way to make Gaussian extension working by doing something? I'...
6
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1answer
98 views

Generating a Gamma centered uniform k mesh in SIESTA DFT

The SIESTA DFT software provides to incorporate a Monkhorst-Pack k grid in DFT calculations. However to use the results with the BoltzTraP2 software, a Gamma centered k-grid with uniform distribution ...
6
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2answers
87 views

Check the syntax of the VASP input file before running

I am a rookie in the DFT calculation area, I found that I could often make mistakes when writing a new input file, so I'd like to ask if there is a tool for checking the syntax and consistency of ...
5
votes
1answer
75 views

Total Energy vs Energy Cut Off convergence

Why is my plot of 'Total Energy vs Energy cut off' is jagged. Previously ecutwfc was kept at 40, 60 and now 80. But still I am unable to figure why isn't it converging. Where as 'Total Energy vs K ...
11
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2answers
567 views

Computational Speed vs multicores

Why is that increasing the number of cores (openMP) in a computation does not decrease the duration of the process? Is it due to consecutive approximation? I took a very simple system of Cu in FCC ...
4
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0answers
37 views

What computational steps needed to characterize the Weyl points?

I am trying to learn the characterization of Weyl nodes computationally. For this, I am using Wannier90 and Z2pack codes in interface with Quantum ESPRESSO. I have done scf, nscf, bands structure, DOS,...
12
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1answer
128 views

Deviation caused by using DFT in Non-Adiabatic Molecular Dynamics

To calculate the excited state properties and processes of semiconductors (e.g. during the photocatalysis process), can be important. Non-Adiabatic Molecular Dynamics (NAMD) is one of the popular ...
4
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47 views

MedeA VASP: Determination of carrier concentration [duplicate]

My question is, how do I calculate the carrier concentration from a DFT study? I am using MedeA VASP for the DFT simulation.
8
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1answer
102 views

Evaluating Seebeck coefficient using DFT

I am working with semiconductor materials using the SIESTA DFT package. I have tried the BoltzTraP2 software interface with SIESTA, however the results (Seebeck coefficient of MgO and Si) did not ...
5
votes
1answer
56 views

Variable Cell Optimization of Halfnium Crystal

Reference: Density Functional Theory: A Practical Introduction, David Sholl, Janice A. Steckel, Chapter 2, Page No. 46 Hf is experimentally observed to be an hcp metal with c/a 1.58. Perform ...
7
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1answer
70 views

Monkhorst – Pack sampling: How many k points one should take

Reference: Density Functional Theory: A Practical Introduction, David Sholl, Janice A. Steckel, Chapter 3, Page No. 59 A useful rule of thumb is that calculations that have similar densities of k ...
13
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1answer
183 views

Doubt about energy convergence with different k points

During the convergence test of k points, I observed my energy start increasing instead of decreasing. I am doubtful is this correct or I am doing something wrong. can I take the appropriate K point in ...

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