Questions tagged [density-functional-theory]

For questions about simulations using Density Functional Theory.

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7
votes
2answers
87 views

Can the NCI (noncovalent interaction) index be generated starting with psi4?

Can NCI[1] index plots be generated starting from psi4? I'd be happy to just generate the NCI index values and mesh the isosurface myself. With a long-term goal to visualise various medicinal-...
11
votes
1answer
114 views

Geometrical Optimization not converging, where am I going wrong?

I am trying to obtain the optical properties of ZnSe Quantum Dots, the problem is that my geometrical optimization is not converging. I used VESTA to create the structure(there is a photo in the ...
12
votes
1answer
632 views

How do we know how much computational power is required for a particular calculation?

So I am super new, although I have gotten the hang of using DFT in Quantum Espresso. I am having a problem with running the calculation for 1.6 nm ZnSe quantum dot. I haven't even gotten to ...
7
votes
0answers
56 views

How to passivate the surface of ZnSe Quantum Dot and apply vacuum to it? [closed]

I have been trying to simulate ZnSe zinc blende quantum dots using Quantum Espresso and its GUI BURAI. But being a beginner I am a little confused about a few things: How do I passivate the surface, ...
7
votes
0answers
55 views

Software for calculating the mirror Chern number of 2D systems?

Can anyone please explain to me how can I calculate the mirror Chern number of a 2D system? I will be very thankful if you can refer me to a package or software which can directly perform mirror Chern ...
11
votes
1answer
269 views

Why is Energy Cut-off and K-Point Convergence necessary in LCAO-based codes like SIESTA?

I am new to DFT-simulation and I wish to understand how it works behind the scene. As the title suggests I don't understand why LCAO-based codes have to define K-points and cut-off energies. I ...
15
votes
1answer
140 views

Linearized Augmented Plane Wave Method vs. Pseudopotential Methods

While reviewing some DFT literature, I have come across a few papers utilizing the LAPW (Linearized Augmented Plane Wave) method, but I am interested in understanding why exactly one would use these ...
10
votes
1answer
220 views

Increasing k-point grid to take DOS calculation

I was trying to compute some electronic properties for Pd using SIESTA and VASP for some computer practicals in my university, specially focused on band structure and density of states (DOS) using LDA ...
13
votes
3answers
554 views

Script to generate input files for benchmark purpose

I would like to run some benchmark of different DFT functionals. The most time consuming part is obviously the generation of the input files. I'm not a programmer, but I think this could be done by ...
8
votes
1answer
177 views

Why volume of unit cell is not the same as cubing the lattice constant?

I have a cubic-FCC with a=b=c and $\alpha$=$\beta$=$\gamma$=$90^o$. As far as I understand the volume of this cubic unit cell should be a cube of the lattice constant. But this not the case I am ...
7
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1answer
83 views

How to choose a different band path for band structure calculation using VASP?

How can I set a different band path for VASP calculation? For example I want to plot KGMK but not GMKG for graphene?
9
votes
1answer
150 views

What is the electrical behavior of the material with this band gap?

Presently I am doing DFT calculations to analyse the electronic structure of a material. I got the band structure as shown in the figure. I would like to know the electrical behavior of this material. ...
9
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0answers
83 views

Is "Valence Electron Density" and "Electron Density" data of a molecule the same thing? [closed]

I'm wondering specifically in the context of calculating physical properties from valence-electron-density data using DFT, MD, and or ML (machine learning).
10
votes
1answer
90 views

Is there a database where one can find the Electron Density data of materials?

The database I am looking for may be experimental, computational or user-generated data. If I end up using the data, I will be providing the necessary citations and credits. Thank You.
10
votes
1answer
102 views

KS-DFT versus G0W0

The central equation that KS-DFT will solve is: $$\tag{1}\left[ -\dfrac{1}{2}\nabla^2+V_{ext}+V_{hartree}+V_{xc} \right]\psi_i(\vec{r})=E_i\psi_i(\vec{r})$$ Here $V_{xc}$ is approximated with LDA or ...
7
votes
2answers
59 views

How to take periodic snapshots while running a simulation in VASP?

Same question, rephrased: What is the procedure to take snapshots at fixed intervals while running an AIMD or DFT Simulation in VASP? OR Which parameter in the INCAR file do I modify to achieve ...
8
votes
1answer
110 views

How to create the structure file for these materials?

I want to create a POSCAR or CIF file file for the monolayers with the data mentioned in the table below : Knowing that the spacegroup is : R-3 (148) Could you please create the POSCAR/CIF for these ...
8
votes
1answer
101 views

How To calculate formation energy of Ni doped ZnO system in Quantum ESPRESSO?

I have successfully completed the SCF of doped system Ni doped ZnO using GGA+U. I have checked the SCF.out file and found the energy value : E= -6112.0389 Ry. Hwo to calculate the formation energy of ...
7
votes
1answer
189 views

How to generate Electron Density Fields using DFT?

How may I generate Electron Density Field information using Density Functional Theory calculations? What would my required inputs be like in VASP or Quantum ESPRESSO?
14
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5answers
706 views

Are dispersion correction methods for DFT (such as D3) useful for geometry optimization?

For what I know the DFT-D3 method or similar corrections that take into account dispersion effect, add this type of contribution through calculation of atom pairwise interactions at the end of an ...
10
votes
3answers
547 views

Which DFT functional should I use to simulate spectra of pesticides?

I am mainly searching for functionals to calculate spectra of pesticides. I found the benchmark test from Goerigk and Grimme$^1$, but don't understand which of the functionals suits my purpose the ...
7
votes
2answers
148 views

Why is there a large discrepancy between calculated frequency dependent dielectric function and experimental measurement?

I am calculating the frequency dependent dielectric function of $\ce{SiC}$ using VASP. After a geometry optimization, the INCAR file below is used for the ...
9
votes
0answers
109 views

How to do a Sampling on the boundary of Brillouin zone in VASP

I use VASP to do my DFT calculation. I have to do a self consistent calculation to generate my CHGCAR. I want to ask is there anyway to write the KPOINTS file to generate K-meshing grid which can ...
7
votes
1answer
61 views

Is it possible to install thermo_pw on windows 10?

For research purpose, my team needs to use thermo_pw package for ab-initio simulations. But the issue we are running into is that we cannot find a way to install it on our computer. We are using ...
25
votes
3answers
1k views

What does B3LYP do well? What does it do badly?

I have seen a general criticism of B3LYP in computational chemistry (especially with the 6-31G* basis set). I would like to know some of the more/less obvious problems that occur when using it and ...
11
votes
2answers
688 views

What is the difference between DOS and PDOS?

I'm new to DFT. Can you please help me to understand DOS and PDOS (projected density of states) in simple wording? I only want to know some basics of these terms and how they are linked to DFT.
9
votes
1answer
155 views

Why VASP calculates the elastic constant for another trigonal space group?

Please, help me to understand the problem. I calculated the elastic constants for the beta PHB (Space group P3221 (154)), it has to show the reduced elastic constant matrix (six), however, ...
12
votes
1answer
62 views

What does this temperature & total free energy profile mean (obtained from VASP NVT molecular dynamics simulations)?

In order to obtain molecular dynamics (MD) simulations trajectory for computing phonon dispersion relation at finite temperature, I performed NVT MD simulation using VASP for my target system. Here is ...
4
votes
1answer
52 views

Optical anisotropy from first-principles

I am interested in the theoretical study of optical anisotropy (birefringence, dichroism etc.) of different materials. I have seen DFT works studying optical anisotropy from the calculation of ...
7
votes
1answer
42 views

How to determine the more stable configuration between a flat and a buckled monolayer with DFT?

Using first principles methods (quantum espresso code) I would like to find if a monolayer of a material is flat or buckled. Using the van der Waals interaction in the calculation I found that the ...
6
votes
1answer
52 views

How to make this DOS plot more smooth and add more points around Fermi level?

I have calculated and plotted the DOS for a doped monolayer 3x3x1 supercell. I want to make the plot more smooth and add more points around Fermi level. Knowing that these are my settings for the ...
8
votes
1answer
80 views

When import volumetric data (spin density of CHGCAR) to VESTA which option should we pick here?

I am trying to plot SPIN DENSITY isosurfaces using VESTA. I have used vaspkit option 312 to create ...
8
votes
1answer
63 views

What is the meaning of element-rich environment in calculating formation energy?

I want to use the formation energy formula used by the article in the picture below. The authors have used the term S or Sn-rich environment. What is the meaning of ...
19
votes
3answers
3k views

Solving the Schrödinger equation as a service?

Does anyone know of a company with a cloud-based service which takes some representation of a molecule as an input, and then somehow solves the Schrödinger equation to some level of accuracy and ...
8
votes
2answers
514 views

Pressure applied DFT calculations in Quantum ESPRESSO

I am trying to perform the pressure-induced DFT calculations in Quantum ESPRESSO. For this, I have calculated the lattice constant of the cubic structure by vc-relax...
8
votes
2answers
330 views

Data format of wannier90_hr.dat from wannier90

I did a calculation on a bulk system with DFT and fit it with the tight binding matrix with wannier90. There is question on this. I try to write my own code to construct a slab tight binding matrix ...
5
votes
2answers
317 views

What is the meaning of these d states names?

I have read in the article at the reference below that : the Mn substitution leads to localized states (impurity bands) within the band gap. The Mn 3d orbitals split into a single a$_1$ (d$_{z^2}$) ...
9
votes
1answer
65 views

Are electron dipolar spin-spin interactions included in DFT calculations?

I am studying point defects in hBN using Quantum ESPRESSO. It is not clear if electron spin-spin interactions are typically/can be included in DFT calculations. I understand that spin-orbit ...
10
votes
2answers
378 views

How can we say that the KS equation is describing a noninteracting many-electron system?

Based on HK's two theorems, the density functional theory was built. Because one can't find the universal energy functional $F_{HK}[n(r)]$, Kohn and Sham further proposed the Kohn-Sham ansatz: mapping ...
10
votes
1answer
98 views

How can I calculate the J value in an antiferromagnetic material?

I am new to DFT, especially in doing DFT for magnetic materials. I recently came across this paper which indicated the calculation of the J value in the case of antiferromagentic materials as per the ...
7
votes
1answer
58 views

PES of Tetramethylthiuramdisulfid / Problem with Disulfidbridge

I like to perform a DFT Study on Tetramethylthiuramdisulfid. So I made a structure optimization for my start structur with PW6B95D3/aug-cc-pvtz to get a good structure to begin my dihedral scan to get ...
10
votes
1answer
124 views

DFT xc integration grid for periodic boundary conditions

I am writing my own DFT code using Gaussian basis and now I am writing the periodic boundary conditions (PBC). What integration grid people usually use for Gaussian basis PBC (+ reference please)? For ...
7
votes
0answers
42 views

Is it possible to construct a tight binding matrix of high atomic layer thin film from the lower one?

Give a tight binding matrix of a few atomic layer thin film system, is it possible to construct a tight binding matrix of higher atomic layers thin film from the lower one? For example, I have a 4 ...
4
votes
1answer
135 views

How to interpret spin density isosurface figures?

The figure below shows the spin density isosurfaces of 3x3x1 ScS2 monolayer supercell doped with Mn atoms. This figure was generated using VASPKIT and ...
6
votes
1answer
309 views

What is the meaning of EATOM tag in the POTCAR files of VASP?

I am wondering what is the meaning of EATOM tag in the POTCAR files of VASP. What is its relationship with the energy of an ...
7
votes
0answers
49 views

Single electron transfer periodic DFT in VASP

I have the following question: I am currently studying the electrocatalytic CO2RR on Cu materials using periodic DFT calculations and I am using the CHE model to describe the proton electron transfer ...
5
votes
1answer
57 views

Divergence behaviour of surface energy

By definition, the surface energy of a thin film or a slab model is defined as $$ \sigma = \frac{1}{2A}(E_{slab} - N\cdot E_{bulk}) $$ where $N$ is the number of atoms in the thin film and $E_{bulk}$ ...
6
votes
1answer
76 views

"A dense k mesh of 40,000 k points was used in the Brillouin zone". How is this number obtained?

In publications, I usually see the statement "A dense k-mesh of 40,000 k-points was used in the Brillouin zone". An example of this is in this paper. But in the paper they have ...
11
votes
1answer
131 views

What does a density of states (DOS) plot show?

I have plotted the density of states using GGA-PBE exchange correlation functional for magnesium silcide but I really do not know what the equations involved are in this process, and how they relate ...
6
votes
1answer
39 views

Where are the atoms located in a charge density calculation using DFT?

The charge density (electron distribution) is calculated self-consistently by employing DFT, so a question arises here: where are the atoms located, or are their positions fixed?

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