# Tag Info

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There are options to include spin-orbit coupling in DFT. In general, there are two ways to do it: Solve Dirac's relativistic equation for the electrons Incorporate relativistic effects through the Pseudopotential Most DFT codes employ (2) as it is easier. There are well tested and readily available 'fully-relativistic' pseudopotentials for LDA and GGA ...

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Even for the simplest transition metal diatomic molecules, the most reliable way to know the ground-state spin configuration is often by doing experiments. I will give an example where it's easy to correctly determine the ground state spin configuration, and then an example where it has remained impossible as of the year 2020. Cr$_2$: Here we can accurately ...

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In the jj-representation, each electron from $i$ to $N$ will have: $\vec{l}_i$ (orbital angular momentum), $\vec{s}_i$ (spin angular momentum), and $\vec{j}_i=\vec{l}_i + \vec{s}_i$ (total angular momentum). In your example we have $N=2$ and both electrons are $p$-type so we have: $$\tag{1} {l}_1=1,~~~~~~~{l}_2=1.$$ Let's also assign the spins for each ...

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Noncollinear magnetism means that the orientation of the magnetization varies in space. Examples for such structures are magnetic domain walls, spin spirals, or magnetic skyrmions. To describe these systems one has to consider the Kohn-Sham wave functions as spinors \Psi_\nu(\mathbf{r}) = \begin{pmatrix} \psi_\nu^{\uparrow}(\mathbf{r}) \\ \psi_\nu^{\... 11 Often when one is asked for the number of spin states, we are interested in determining the spin state of metal complexes containing these ions, rather than the lone ion itself. If you are interested in just the lone ion itself, Nike Dattani's answer goes into depth about that. My answer will focus on the determination of spin states of ions within metal ... 11 \ce{Cu}^+ This ion has 28 electrons. If all of them are up (i.e. aligned with the +z axis), then since each electron has a spin of magnitude 1/2, we would have a total spin of +14. If all of them are down we would have a total spin of -14. We could also have 1 up and 27 down, meaning +\frac{1}{2} - \frac{27}{2} = -\frac{26}{2} = -13. The number of total ... 10 Basically, this is the split between restricted, unrestricted, and generalized Hartree-Fock (or Kohn-Sham) theory. In the restricted theory, both the spin-up and spin-down electrons occupy the same spatial orbital: \psi_{2n}({\bf r}) = \phi_n ({\bf r}) |\uparrow \rangle, \psi_{2n+1}({\bf r}) = \phi_n ({\bf r}) |\downarrow \rangle. This is the Ansatz you ... 9 Pseudopotentials (PPs) describe the effective interaction between the valence electrons and a nuclei screened by frozen core electrons. This approximation makes DFT calculations less computationally expensive as only valence electrons are treated explicitly and the resulting valence wavefunctions no longer oscillate rapidly near the cores to ensure ... 8 I wouldn't recommend that you go above 10^{-8}, what you have in your current calculation. With SCF calculations, you definitely need a lower convergence threshold compared to say relaxing procedures. I suspect your problem is rooted elsewhere. Try: Lowering 'mixing-beta' Removing 'verbosity' as it just prints energy levels and takes up time, which you ... 8 If you're studying transition metal complexes, in short, there is no way to know except for to try the relevant physically plausible spin multiplicities and take the lowest energy solution as the ground state. For instance, an Fe(II) complex can have up to 4 unpaired electrons since it is 3d^6. This is what we call the high-spin state and would be 2S+1=3.... 7 As far I understand, to search for spin-polarized solutions, the DFT code will have to solve two coupled Kohn-Sham equations, one for each of the two spin species. There is both direct and indirect coupling between the two Kohn-Sham equations . The direct coupling comes about by the dependence of the effective potential in the Kohn-Sham equation ... 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 Spin-orbit coupling is related to relativity which is increasingly important for heavier elements. If you're aiming for ultra-high precision, as in this post on our site: How accurate are the most accurate calculations?, you will need to include every possible effect, including spin-orbit coupling, for all elements including hydrogen. For most applications, ... 6 This error has been resolved now. Though I am not an expert but here are few thoughts. There may be several reasons for this error: This error might appear due to numerical instability from overlapping atoms. As mentioned by @Phil Hasnip, if the S-matrix eigenvalues are really small. Some pseudopotential may not fit with calculation, USPP giving non-... 6 But in the case of the pseudo-potentials included, should I use fully relativistic pseudopotentials for all three elements? Yes, you should use the fully relativistic pseudopotentials if you are considering spin-orbit coupling calculations. When you should consider spin-orbit coupling? If the investigated materials contain heavy atoms then you should ... 5 Extracting the spin density should supposedly be as simple as reading the CHGCAR and extracting the X Y Z density separately (It is all output). You can then treat this the same way as spin up / down. As a bonus, if you can link a reasonably sized non collinear CHGCAR somewhere I may be able to make you something to split it for you. Source: Vasp Forums 5 Spin-orbit coupling scales as Z^4/n^3 where Z is the atomic number and n is the principal quantum number. When you move down the periodic table and the nucleus becomes heavier and heavier, relativistic effects become more important. From a practical approach, when should you start incorporating SOC in your DFT calculations? From my experience, that cut-... 5 A complete input card is given for the previous post about HSE06+SOC band structure calculation. Step-I: DFT SCF calculation with SOC (INCAR): System=XXX ISTART=0 ICHARG=2 ENCUT=400 EDIFF=1E-6 NELM=300 ISMEAR=-5 #SIGMA=0.05 ... 4 "However, I am stumped on the definition of H_{SO}=\lambda_{SO} L\cdot S. What is L\cdot S?" Spin-orbit coupling is typically written as a scalar coupling constant (in this case \lambda_{\textrm{SO}}) multiplied with \hat{L}\cdot \hat{S} where \hat{L} is an orbital angular momentum operator and \hat{S} is a spin angular momentum ... 4 Here I show the typical calculation flow of GW in VASP: a DFT ground-state calculation. obtain DFT virtual orbitals GW calculation including LWANNIER90 TAG Compute Wannier functions and Obtain bandstructure by Wannier interpolation. PS1: use POTCAR like [XXX_GW]. PS2: If you want to include spin-orbit coupling, just add the following tags: LSORBIT=.TRUE.... 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 And I couldn't find any example of SOC being considered for Magnetic systems. There are many examples that consider the effect of SOC in magnetic systems. For example, the monolayer LaBr_2 in this paper, in which the author compares the band structures for three cases as follows: A bulk case also could be found in this paper: Phys. Rev. Lett. 122, 206401 ... 4 Spin-orbit coupling is an effect that is dependent on the relativistic effect. So you should use fully relativistic PP(pseudopotentials) whatever you use. Another thing is that PP often varies from your material structure. So, the efficiency of PP is highly dependent on what your simulation output parameter is. There are a lot of things related to the ... 3 The spin-orbit effect is something that your code has to be able to do, it is not a property of the pseudopotential. Here you can find other discussions about it: How to incorporate the effect of spin-orbit coupling in electronic structure calculation Spin–orbit interaction with DFT 3 Here are some possible changes to your input that may resolve the problem: Your EDIFF is very small; use the default and then increase precision from there. Use a smaller SIGMA, start with 0.15 or 0.1. Decrease the number of k-points, start with 5x5x5, then increase to reach the desired precision. Good luck! 3 How to change the spin-orbit coupling strength in VASP? Firstly, one can't realize this just by changing the input parameters in the INCAR for VASP. To tune the strength of spin-orbit coupling in VASP, you need to modify the source file vasp_source_code_path/src/relativistic.F and recompile it. For example, if you want to reduce the strength to half you can ... 2 VASP with the PAW method can't take a fully relativistic effect, which can be taken into account only by solving the Dirac equation. The SOC effect in the PAW method is included with the following perturbed Hamiltonian (zeroth-order-regular approximation):$$H_{SO}^{\alpha\beta}=-\dfrac{\hbar^2}{(2m_ec)^2} \dfrac{K(r)}{r}\dfrac{dV(r)}{dr}\vec{\sigma}^{\alpha\...

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If you are considering SOC, which means the noncolinear calculations are performed. I assume that the eigenstate of the Kohn-Sham equation is labeled by $|atom, k, orbital, spin \rangle$. To obtain a spin-polarized band structure, you should do a fat band analysis with the consideration of the different spin components: \$\langle atom, k, orbital, spin|s_x \...

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As a beginner and to the best of my knowledge spin-orbit coupling is irrelevant to the magnetic properties. Spin-orbit coupling is related to relativity which is increasingly important for heavier for elements around Krypton and onward, and also if you're aiming for high precision. For convergence, try to increase electron_maxstep >> 100 (maximum ...

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