Questions tagged [density-functional-theory]
For questions about simulations using Density Functional Theory.
571
questions
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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 ...
5
votes
0answers
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 ...
5
votes
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 ...
7
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0answers
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
votes
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
votes
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
votes
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
votes
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?...
6
votes
0answers
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 ...
5
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0answers
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
votes
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
votes
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
votes
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 ...
4
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0answers
31 views
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
5
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0answers
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
votes
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?
4
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1answer
62 views
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
votes
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 ...
3
votes
0answers
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
votes
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
votes
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 (...
5
votes
0answers
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 ...
9
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0answers
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
votes
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 ...
6
votes
0answers
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
votes
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
votes
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
votes
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
votes
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 ...
6
votes
0answers
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
votes
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
votes
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 ...
4
votes
0answers
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
votes
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
votes
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
votes
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
votes
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
votes
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
votes
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
votes
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
votes
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
votes
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
votes
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
votes
0answers
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
votes
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
votes
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
votes
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 ...