# Questions tagged [density-functional-theory]

For questions about simulations using Density Functional Theory.

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11 views

### How to analyze the band symmetry with Quantum ESPRESSO?

This question is related to this paper: J. Phys. Chem. Lett. 2017, 8, 13, 2999–3007 The above figure shows symmetry analysis for the band structure. The author writes: The band symmetry and parity ...
15 views

### Relax vs VC-Relax for interstitial incorporation energy

In order to model an interstitial trapped in a metal lattice, and the associated incorporation energy, which should be used - "relax" or "vc-relax"? I want to understand the ...
49 views

### Calculating hyperpolarizability in NWChem

I'm trying to make a pipeline geometry optimization -> calculation of polarizability/hyperpolarizability. And NWChem seems pretty good for it, the only thing I can't understand its how to calculate ...
24 views

### Is there a difference in performance when the symmetry is specified via ibrav in Quantum ESPRESSO?

I have been using cif2cell for converting CIF files into quantum ESPRESSO input files. But cif2cell always keeps the ibrav value to be zero and indicates the CELL_PARAMETERS. As per the quantum ...
31 views

### Are there other kinds of stability of materials? How to demonstrate that with computation approaches?

I have known some kinds of stability of materials, such as: Mechanical stability; Dynamical stability; Thermal stability In particular, they can be studied with first-principles computational ...
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225 views

### How does libxc calculate the potential of GGA functionals?

If the GGA xc energy is defined as $$E_{xc}[n] = \int n(\mathbf{r}) \varepsilon_{xc}[n(\mathbf{r}), \nabla n(\mathbf{r})]\ d\mathbf{r},$$ the potential can be written as  V_{xc}[n] = \varepsilon_{...
41 views

### How to proceed with learning application of Machine Learning in material modelling?

This might be very broad question. Since ML application in Matter Modelling is emerging field it would good to understand how it is applied and why it is useful.
420 views

### What is nscf calculation in Quantum ESPRESSO?

I have been using 'nscf' for DOS calculation since it is faster and therefore possible to use a higher kpoints. But why is it faster? why not use it in the place of 'scf'?
88 views

### How to calculate the potential in Hubbard-U correction and when to apply it?

I have seen that in certain cases Hubbard-U correction is relevant yet I have seen a number of papers that have not used it. So, I want to know if there is any theoretical basis for finding this ...
89 views

### Calculating the band structure with different unit cell

I have to do a electronic band structure calculation on a heterostructure using DFT calculation. First I do the calculation on each phase separately. I use a primitive unit cell to do the calculation ...
226 views

### Plotting density of states of Fe(BCC) using Quantum ESPRESSO

I have run the DFT calculation and plotted DOS of Fe(BCC) in Quantum ESPRESSO. I have attached the plot: (click on image to see clearly) But It's a wrong plot as it is not matched with the referenced ...
72 views

### Isotopes in Reaction Kinetics by Transition State Theory

Can kinetic isotope effects be handled in density functional theory level calculations? My intuition says that in the context of molecular dynamics simulations that they can be, but can transition ...
181 views

### Spin orbit coupling from spin polarized density of states?

My knowledge in these areas of physics is lacking, so please expect naivety ahead (perhaps, dumb down your answer accordingly). From what I read online, spin orbit coupling is how the angular momentum ...
249 views

### Does One-to-One Correspondence of Hohenberg Kohn Theorem Mean Bijective or Injective and How to Prove it?

I have asked a similar question but after thinking about it I have a more specific question. According to Ullrich, Carsten A.. Time-Dependent Density-Functional Theory : Concepts and Applications, the ...
73 views

### Determine DFT+U values by linear response

I am currently trying to determine how DFT+U values can be determined self consistently. I see that the bare and converged linear response matrix contain the difference in occupancies from the ground ...
196 views

### Create doped structures to POSCAR files for vasp

I have a perfect supercell structure Ni fcc. And I would like to dope another element O or N with a ratio of O:Ni=8:100 to the supercell of 3x3x3 and find the most stable ordering structure. The ...
119 views

### Comparing calculations in plane wave and atomic orbital bases for the same functional

Let's say I have two codes. One is plane wave, and the other is using atomic orbitals as basis sets. How can I compare these two codes with the same functional? And let's say I want to optimise the ...
80 views

### Apply DFT+U to Oxygen/Nitrogen p Orbitals

I often see DFT+U corrections for transition metals with delocalization problems, but a comment about applying a U correction to nitrogen or oxygen's p orbitals also shows up when digging around in ...
156 views

### How can I do a charge transfer study in bulk crystalline materials?

Let's say a supercell has 100 atoms, and we want to see how charge is transferred from/to an atom to/from its nearest neighbours. I am more interested in knowing how to do this with density functional ...
50 views

### How can I increase the default maximum limit on step size for convergence in quantum ESPRESSO?

When trying to manually optimise the geometry of the crystal, I've faced an issue wherein the code stopped the convergence process after just 100 steps (which was the default maximum). Is there a way ...
112 views

### How to use the ev.x tool in Quantum ESPRESSO?

The requirement I have is to calculate the bulk modulus from the Energy values at certain Volumes obtained via DFT calculations. Can you provide the instructions to use the ev.x tool in the Quantum ...
46 views

### Converge number of layers of atoms or number of unit cells for adsorption calculations?

I'm trying to calculate the adsorption energies of various adsorbates on Fe2O3 surfaces (although, with there being many possible surfaces for Fe2O3 it is quite complex, but that's for another time...)...
60 views

### Electron Affinity of Semiconductors via DFT

Can we calculate electron affinity of a semiconductor (e.g., for Si) using density functional theory calculations in VASP? Which calculations are needed to compute electron affinity and band offsets?
498 views

### Is there a list of all functionals?

A quick google search of the Minnesota Functionals will lead you to the wikipedia page on them where it will state the following: ...
65 views

### Fermi energy in density functional theory

Disclaimer: Assume the questioner is a novice in DFT and condensed matter physics in general. How reliable are DFT based estimates of the fermi energy? Do different flavours of DFT affect the accuracy ...
158 views

### What are the pitfalls of calculating band gaps via density functional theory?

There are various questions on this SE that discuss DFT in terms of band gaps - here, here, here, and elsewhere - but they touch upon different aspects. Cautionary note: I'm asking this from the mind-...
63 views

### Quantifying electronic overlap?

I am trying to understand how to quantify the electronic interaction/conduction/overlap between two metal cores at varying distances. As someone who works primarily with classical MD, and has less ...
164 views

### How to set vacuum space for slabs?

Let's say I want to work with the slabs, and I want to add 20 Angstrom vacuum space. Do I need just to set lattice parameter c=20 and k-point 1 in this direction?
86 views

### The projector augmented wave (PAW) method, pseudopotentials (PP), and exchange correlation functionals

Disclaimer: Assume the questioner is a novice in DFT Is PAW an improvement over the pseudopotential method? In terms of Perdew, Burke, and Ernzerhof (PBE) parameterization, what is the difference ...
144 views

### What can we learn by inspecting charge densities calculated with DFT?

The charge density is an important physical quantity obtained from first-principles calculations based on density functional theory (DFT). Much useful information about the investigated materials can ...