# Tag Info

13

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 Brillouin zone (BZ). If you calculate $g(E)$ in the primitive cell, then you will integrate over the primitive cell BZ. If you calculate $g(E)$ in a supercell, then ...

9

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 about "bonding character," as you mention in your follow-up comment. If you are specifically interested in "bonding character" when using a ...

9

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 $E_{n\mathbf{k}}$ are the electronic energies and the integral is over the Brillouin zone. There are various strategies that one can follow, including: ...

8

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 eV. Set EMIN=Fermi-5 and EMAX=Fermi+5 Set NEDOS=Anything Odd As a rule, you should always hit the middle point doing this and the middle point is the Fermi ...

8

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 material is a metal (zero gap), a semiconductor (gap greater than zero and lower than $\sim 3eV$ or insulating (gap $> 3eV$). To identify the conduction/valence ...

8

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 by setting ISPIN=2). Using the relaxed structure to perform the electronic self-consistent calculation to obtain converged charge density [2scf]. Using the ...

7

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 don't need to re-relax the structure (Step #1). You should be able to read in the charge density and set ISYM=0 (symmetry disabled) and be okay. Disclaimer: ...

7

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 use nspin=2, you are saying that you will define the initial magnetization for the involved species. So, just keep in mind that spin-polarized calculations will ...

7

From the SUMO DOS documentation page we have that the option --no-shift controls when to shift the Fermi energy or not: --no-shift don’t shift the VBM/Fermi level to 0 eV Default: True In the case of P4VASP, from its page related to plotting DOS: In all DOS/bandstructure graphs is the energy relative to the Fermi energy - i.e. the Fermi energy on ...

7

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 with its spin. Yes, and there are two types interactions Russell Saunders coupling(LS coupling) and the j-j coupling. The electron has an orbital angular ...

7

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 to be occupied by the system at each energy. The density of states is defined as $D ( E ) = N ( E ) / V$ , where $N ( E ) \delta E$ is the number of states in ...

7

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 crystal field splitting energy of the S ligand around the TM atoms" I can see why you had to ask this question here, because when I search "d-orbital spin-...

7

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, semiconductors, metals, semimetals, and half-metals based on the electronic band structures (density of states or band structure), as shown below. (a): Metal (b)...

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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 wavefunctions of the two states involved in the transition and $\mu$ the transition operator. This integral represents the transition probability ($P_T$). When the result ...

6

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 monolayer CrI$_3$. To achieve an AFM configuration, a square lattice with four Cr atoms is built as follows: Antiferromagnetic configuration setting: Cr1 ($\... 6 There is a great description given of COOP in Roald Hoffman's Solids and Surfaces: A Chemist's View of Bonding in Extended Structures. It is sometimes referred to as the Overlap Population Weighted Density of States (OPWDOS) which makes the meaning a bit clearer: its the density of states, weighted by the overlap for a given bond ($c_ic_jS_{ij}$). This ... 6 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 periodic solids. The quantum state for solids can be formally expressed as: $$|atom, k, orbital,spin\rangle$$ The band-gap can be considered as global information ... 6 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: you don't want to do that. Supercells are typically needed when studying non-periodic systems using calculations with periodic boundary conditions. These could ... 6 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 level is set to VBM. 5 There are many applications/advantages for supercell band unfolding. Take the band unfolding program KPROJ as an example: Nano Lett. 14, 5189 (2014) A k-projection technique (supercell band unfolding) that includes the$k_\perp$-dependence of the surface bands is used to separate the contributions arising from the silicene and the substrate, allowing a ... 5 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 containing the wavefunctions (Kohn-sham orbitals), charge density, etc. This can be done in two different ways during the parallelization: collected: all files from ... 4 What is spin-orbit coupling (soc) and what does soc strength mean? The spin-orbital coupling (SOC) is a relativistic effect. Mathematically, it can be represented as: $$\vec{L} \cdot \vec{S}$$ in which$\vec{L}$is orbital angular momentum and$\vec{S}$is spin angular momentum. How to identify the strength of SOC? Taking the Hamiltonian without the ... 4 The density of states (DOS) is the number of different states at a particular energy level that electrons are permitted to occupy, i.e. the number of electron states per unit volume per unit energy. It is usually summarized by the equation $$DOS = (\frac{dN}{dE})$$ Since the first derivative of N with respect to E exists, you can, in fact, interpolate the ... 4 If the system is magnetic you need to use nspin=2. You can use any pseudopotential, unless you want to see SOC, in which case you need to use a fully relativistic pseudopotential. 4 In order to do that, you need to use the Partial Density of States (PDOS) were you can have the contribution of each atom/orbital to the DOS. 4 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 field theory, you will usually see the phrase pairing energy rather than "spin-splitting". The distinction is basically just the direction, where the ... 4 For calculating DOS in VASP, Relaxed the structure first using ISIF=3 (volume and atom position relaxation) followed by SCF calculation for generating charge density. In the third calculation use LORBIT=11/12 with ISTART=11. VASP ignores RWIGS parameter for LORBIT>=10,hence no need to change that. Use the ISMEAR parameter wisely. 4 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\phi_n(\vec{r}) \end{equation} Here$v_{ks}$represents the KS effective potential and$n=(atom, orbital, k, spin)\$ the collective quantum number of the quantum ...

4

To answer your first question: the theory has certainly been worked out in some detail. The most accurate approach (a) would involve a quantum transport calculation in the non-equilibrium Green function formalism, describing the tip (L) and the sample (R) as semi-infinite leads, connected by a central region (C), and using the Meir-Wingreen formula to ...

4

Neither the valence band maximum (VBM) nor the conduction band minimum (CBM) have to be at a k-point from the k-point set that you use for an SCF, DOS, or band structure calculation. I don't know what VASP reports as the Fermi level for insulators, but I guess that it is the energy of the highest occupied state within the used k-point set. Since it is not ...

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