14
votes
Accepted
Density of States of Supercells
The density of states reads:
$$
\tag{1}
g(E)=\sum_{n}\int\frac{d\mathbf{k}}{(2\pi)^3}\delta(E-E_{n\mathbf{k}}),
$$
where $E_{n\mathbf{k}}$ are the electronic energies and the integral is over the ...
- 10.9k
11
votes
Accepted
Validity of interpolation for density of states?
Calculating densities of states is a tricky problem, as you correctly recognized. The density of states is:
$$
\tag{1}
g(E)=\sum_{n}\int\frac{d\mathbf{k}}{(2\pi)^3}\delta(E-E_{n\mathbf{k}}),
$$
where $...
- 10.9k
11
votes
How to model an anti-ferromagnetic crystal in quantum ESPRESSO properly?
The key point is the setting of starting_magnetization. You can find an explanation on the pw.x input description page.
Here I give you an example to set this tag. The structure picked here is the ...
- 14.9k
10
votes
Properties that can be deduced from Band structure and DOS
Some of the properties we can get from the band structure are:
Band gap: energy between the bottom of the conduction band (CB) and the top of the valence band (VB). The gap will give you if the ...
- 22.3k
10
votes
What is the difference between DOS and PDOS?
From the Wiki (a good starting point):
DOS (Density of State):
In solid state physics and condensed matter physics, the density of
states (DOS) of a system describes the proportion of states that are
...
- 22.3k
9
votes
How to analyze density of states?
As noted by @Camps, you can gain a lot of information from a projected density of states by looking at the contribution of a given orbital. However, it won't directly tell you a lot of information ...
- 7,281
8
votes
Properties that can be deduced from Band structure and DOS
I would like to add some information to Camps's answer. In essence, the band structure should consider the information about each quantum state obtained by solving the Kohn-Sham equation for the ...
- 14.9k
8
votes
Effect of ISYM tag on Partial Density of States (VASP version < 6)
The typical calculation flow for the density of states is:
Geometric relaxation to obtain the lowest-energy structure (CONTCAR) [1relax] (For your system, you should do the spin-polarized calculation ...
- 14.9k
8
votes
Find the value of density of states at the Fermi energy using VASP
Let me suggest a simple answer, although I am not convinced you will get anything sufficently different for the fermi level than just using a converged grid.
Consider a range of energies such as 10 ...
- 10.8k
8
votes
What do we mean by spin-splitting energy?
The word "splitting" seems to occur only in one sentence, over the course of the entire paper that you referenced:
"The d-orbital spin-splitting energy is stronger than the weak ...
- 33.6k
8
votes
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If Gaussian and Tetrahedron smearing method lead to different Fermi energies, which one is the correct?
ISMEAR=-5 gives you the correct Fermi energy.
Usually, the Fermi level is set to the VBM.
If you shift the BS by the Fermi energy from the DOS calculation with ISMEAR=-5, you will find your Fermi ...
- 14.9k
8
votes
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Why am I getting DOS like this in Quantum ESPRESSO?
I suspect that these are the $5s$ and $5p$ states of $\ce{Hf}$, which are treated as valence in the pseudopotential you're using. These states will be fairly tightly bound to the nucleus, which always ...
- 6,582
7
votes
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Does the DOS plotted by p4vasp already have Fermi energy subtracted?
From the SUMO DOS documentation page we have that the option --no-shift controls when to shift the Fermi energy or not:
...
- 22.3k
7
votes
Spin orbit coupling from spin polarized density of states?
I'll try to be as basic as I can in regard to explaining the stuff youve posted.
From what I read online, spin-orbit coupling is how the angular
momentum of an electron w.r.t. the nucleus interacts ...
- 4,448
7
votes
Should I do vc-relax with nspin=2 in Quantum Espresso for magnetic samples?
It is a bit difficult to answer this question, due to the information provided. If you are a beginner, using vc-relax will have its pros and cons.
With regards to using nspin=2:
Recall that when you ...
- 4,719
7
votes
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Effect of ISYM tag on Partial Density of States (VASP version < 6)
Based on the comments I shared above, it seems that the quality of the charge density is fine. It is just the projection onto atoms that may not be done correctly. If this is indeed the case, then you ...
- 7,281
7
votes
What is the difference between DOS and PDOS?
Basically, the central job of KS-DFT is to solve self-consistently the following non-colinear KS equation:
\begin{equation}
\left[ -\dfrac{1}{2}\nabla^2+v_{ks}(\vec{r}) \right]\phi_n(\vec{r})=E_n\...
- 14.9k
7
votes
Accepted
What is the difference between a half metal (HM) and a spin gapless semiconductor (SGS)?
The concept of spin gapless semiconductors (SGS) was proposed in this paper: PRL 100, 156404 (2008).
In quantum solid-state band theory, materials in nature are generally classified as insulators, ...
- 14.9k
7
votes
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Does SCF calculation have to be done before calculating DOS?
The community wiki by Tyberius is a bit misleading here, you are not doing molecular dynamics calculations (IBRION=0) but likely a geometry optimization (IBRION=1,2,3). In the case of geometry ...
- 10.8k
7
votes
Why don't we use the principal quantum number when building the projected density of state?
I think this issue is avoided in practical sense. I am not sure any of the psuedopotentials provided with VASP actually include valence electrons of the same angular momentum (so you never have 3s ...
- 10.8k
7
votes
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Why don't we use the principal quantum number when building the projected density of state?
I think the reason is many-fold. In addition to what Tristan mentioned, there are some other possible reasons:
The principle quantum number is a relatively ill-defined concept for an atom in a ...
- 9,076
7
votes
Does integrating PDOS give total charge of a system?
You shouldn't integrate to the Fermi energy, unless you want the T = 0 K result and that was what you computed with your DFT program (which is actually quite difficult to get).
The correct expression ...
- 6,582
7
votes
Accepted
Why do we not get DOS by summing over all the PDOS?
The fundamental problem is that the basis set used for the partial density-of-states (PDOS) does not span the plane-wave basis set space, so it is not usually possible to represent the Kohn-Sham ...
- 6,582
6
votes
Accepted
What's the crystal orbital Hamiltonian population?
There is a great description given of COOP in Roald Hoffman's Solids and Surfaces: A Chemist's View of Bonding in Extended Structures. It is sometimes referred to as the Overlap Population Weighted ...
- 15.2k
6
votes
Accepted
Supercell band structure unfolding advantages
Some reasons why you may want to do band unfolding have been explained by Jack. What I would like to add here concerns your second question about doing band structure calculations in the supercell: ...
- 10.9k
6
votes
Accepted
Spin considerations for the bandgap and optical excitations
I don't think we need to talk about driving forces (this sounds esoteric) instead calculating the selection rule:
$$P_T = \int \psi_1^* \mu \psi_2 d\tau$$
Here $\psi_1$ and $\psi_2$ are the ...
- 22.3k
6
votes
Accepted
Can I run an nscf calculation in Quantum ESPRESSO with disk_io='none'?
Eventually, I figured out what was wrong happening with my DFT calculation. As I understand now, each processor saves and maintains (write recursively as the calculation progresses) its own file ...
- 2,561
6
votes
How does electronic iteration work in a VASP relaxation calculation?
The figure below represents very well the self-consistent field (SCF) procedure used to solve the Kohn-Sham (KS) equations under the Density Functional Theory (DFT) approach:
I think that this ...
- 22.3k
5
votes
Accepted
What do we mean by spin-splitting energy?
I see now how your initial questions were related, as they all fall under the scope of crystal field theory. I wrote a bit about this in a previous answer.
At least in the context of molecular crystal ...
- 15.2k
5
votes
Accepted
Band structure and density of states disagreement (mp-19092)
In short, you can't completely believe the data supported by the Materials Project.
Specific to the Co2W2O8 entry, there are many self-contradictory points shown on their webpage. This can be seen ...
- 14.9k
Only top scored, non community-wiki answers of a minimum length are eligible