Questions tagged [density-functional-theory]
For questions about simulations using Density Functional Theory.
300
questions
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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 ...
6
votes
0answers
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 ...
7
votes
1answer
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 ...
2
votes
0answers
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 ...
2
votes
0answers
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 ...
4
votes
0answers
37 views
Equations related to the first order derivative of the wave function
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 \...
6
votes
1answer
47 views
How to choose starting magnetization while doing spin polarised calculation in Quantum ESPRESSO?
I am trying to run spin polarised DFT calculation in Quantum ESPRESSO on system Co2MnSi. I kept starting magnetization for all these three species as,
...
6
votes
1answer
32 views
How can I assign spins to an non-planar Anti-Ferro Magnetic system (CoO in this case)?
I have been working with an anti-ferromagnetic material Cobalt Oxide. And in the image given below the blue spheres are Co ions. The blue spheres form a tetrahedron shape.
And I've assigned the spin ...
7
votes
1answer
30 views
7
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1answer
77 views
What differences are there when modeling metal-organic-frameworks as isolated clusters or periodic solids?
Should I take MOF (metal-organic framework) as a periodic structure or an isolated cluster? What's the difference between them? If it's periodic, can I do an analysis of the electronic structure, such ...
6
votes
1answer
141 views
Where to obtain MOF structures suitable for carrying out DFT simulations?
For bulk and two-dimensional materials, we can download the structures from many databases, such as Materials Project and CMR. Are there also similar databases for MOF (metal-organic framework) ...
8
votes
1answer
129 views
What are the pitfalls for the simulation of MOF materials with VASP?
I want to study the properties of metal-organic framework (MOF) materials with DFT implemented in VASP. What's the pitfall for this kind of simulation? Which points should I take special care of?
I ...
9
votes
0answers
63 views
Geometric optimization taking a long time. Are my convergence criteria too tight in CP2K?
I have been having trouble with the VIBRATIONAL_ANALYSIS routine. Namely, the routine keeps timing out. I am trying to find the vibrational modes of Pyridine in a non periodic system, as well as Mo2C ...
14
votes
1answer
139 views
Which codes can perform density functional perturbation theory (DFPT) calculations for a van der Waals (vdW) material?
I notice that most codes can only perform finite difference calculations when including van der Waals interaction. Are there any codes that can apply density functional perturbation theory (DFPT) in ...
12
votes
1answer
99 views
What's the physics contained in the exchange-correlation functional in the framework of KS-DFT?
This question is inspired by this post. In the Kohn-Sham framework of density functional theory, the total energy is expressed as:
$$E=E_{kin}^{non}+E_{ext}+E_{H}+E_{xc}$$
in which
The first term is ...
11
votes
0answers
89 views
First order variation of the wave function
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_{...
8
votes
0answers
113 views
General features of pseudogap in the DoS of metals?
Total DOS is used for showing number of energy states at different energies close to fermi level. It gives ideas about system characteristics. We often encounter pseudogaps near fermi level in DOS ...
10
votes
1answer
53 views
How to model an anti-ferromagnetic crystal in quantum ESPRESSO properly?
I'm fairly new to DFT. I would like to plot the DOS and band structure of Cobalt Oxide (CoO). But since CoO is anti ferro magnetic, how would I approach the problem? would I create an input file ...
8
votes
1answer
60 views
How to remove HSE06 bandstructure fake k-points from vasprun.xml file?
Is there any script that can remove fake k-points from a vasprun.xmlfile for HSE06 bandstructure calculation? because removing it manually is a time consuming task.
5
votes
0answers
49 views
Photoemission Spectra of Solids
I know that in non-periodic codes such as Gaussian the fluorescence spectra of molecule can be calculated in the following manner.
Relax geometry
TD-DFT to find excited state
Relax excited state ...
8
votes
1answer
119 views
Spin polarized DFT calculation in Quantum ESPRESSO
I am trying to run spin polarized DFT calculation on system Ti2FeSn.
I am doing vc-relax calculation to relax the unit cell but having problem to converge total energy. Total magnetization is also ...
5
votes
0answers
47 views
Reading in E-field with CP2K
I have figured out a way to input a custom electric field in a .cube format, but I am not sure I am doing it in the proper way. Currently my file contains information for the magnitude of the electric ...
7
votes
0answers
81 views
Orbital magnetization in periodic solids
The orbital magnetization in periodic solids has been nicely described by the so-called modern theory of magnetization [1,2,3,4].
$$\tag{1}
\mathcal{M}_{orb} = -\frac{1}{2} \Im \sum_{n,\mathbf{k}} f_{...
9
votes
1answer
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_{...
3
votes
1answer
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.
13
votes
2answers
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'?
6
votes
1answer
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 ...
5
votes
2answers
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 ...
9
votes
2answers
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 ...
8
votes
1answer
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 ...
9
votes
2answers
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 ...
10
votes
1answer
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 ...
8
votes
1answer
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 ...
11
votes
4answers
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 ...
11
votes
2answers
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 ...
7
votes
2answers
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 ...
8
votes
2answers
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 ...
5
votes
2answers
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 ...
5
votes
1answer
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 ...
7
votes
0answers
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...)...
7
votes
1answer
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?
9
votes
2answers
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:
...
9
votes
1answer
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 ...
8
votes
2answers
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-...
9
votes
2answers
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 ...
9
votes
1answer
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?
3
votes
1answer
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 ...
10
votes
1answer
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 ...
5
votes
1answer
56 views
How to resolve the cif2cell TypeError?
I have encountered an error using cif2cell while covering a CIF file from COD to quantum ESPRESSO format. The error is as follows.
command typed:
$cif2cell crystal.cif -p quantum-espresso -o crystal....
13
votes
0answers
114 views
Promising functionals for transition metal chemistry
I'm looking to get your opinions on the most promising density functionals to use for thermochemistry and kinetics of transition metal complexes. However, as eloquently laid out by Tom Manz on this ...
