Questions tagged [condensed-matter]
For all matters related to condensed matter physics.
100
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Kohn anomaly and avoided crossing (or anticrossing/level repulsion)
Kohn Anomaly and Avoided Crossing (Anticrossing/Level Repulsion) are terms that are found to be used when discussing phonon dispersion. The former (see last paragraph, page 198) is related to electron-...
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2
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How to increase the number of CPUs in my computer?
I'm running my calculations using Quantum ESPRESSO on a 10th generation i7 computer (Dell) with Ubuntu.
When I run any calculation using the command ...
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2
votes
0
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What software can simulate bulk magnetism?
I am interested in investigating bulk magnetism computationally. What are the packages available for it? Any help in this direction will be appreciated.
Please answer with the format of the answer in ...
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0
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Is it possible to evaluate rotational and vibrational partition functions for diffusion in the Eyring Theory of Absolute Rates?
Let us consider the usual expression for Diffusion processes and diffusion coefficients in the Eyring's theory:
$$D=\lambda^2k = \lambda^2 \frac{k_BT}{h}\frac{\Omega_\ddagger}{\Omega}e^{-\frac{\...
3
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Original reference for gapped chiral fermion k·p model?
In eq. 1 of this reference, the authors present the following Hamiltonian for the 2-band gapped chiral fermion model that can describe many systems including various semiconductors, N-layer graphene, ...
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8
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1
answer
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Screened Coulomb interaction and its direct Fourier transform
I have a question concerning the screened Coulomb interaction in periodic systems.
Many first-principle DFT codes provide the possibility to compute linear response functions, such as the irreducible ...
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4
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0
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48
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When the T-even and T-odd conductivity tensor indicates the dissipationless transport?
In this paper, the authors discuss the three response relations or Ohm's law for spin/charge transport. The first one is the spin Hall effect described by:
$$J_j^i=\sigma_{s}\epsilon_{ijk}E_k \tag{1},$...
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3
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Symmetry for the low-energy effective model of Weyl semimetal
The low-energy effective model for Weyl semimetals (WSM) at a single Weyl point can be written as:
$$H_{w}=\chi \vec{k} \cdot \vec{\sigma}, \tag{1} $$
where $\chi$ is the chirality index, $\vec{k}$ is ...
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1
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1
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Is it possible to define a property like strain to characterize the structural change?
Lets suppose that I have an atom chain like system 1 below. Now, some interaction made one atom to move out of the chain, like shown in system 2 (the moved atom remains bounded but in another position)...
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How to plot downfolded bands from DFT bands?
Once you mapped the high symmetry points from primitive cell to the super cell, you need to plot the downfolded bands.
As we know in DFT output of band structure calculation we get a set of E vs k ...
- 113
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Is there any relation between electride and an electron localization function (ELF)?
I would like to know if there is any correlation between the ELF values with materials in the electronic phase, versus with the electride phase?
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Invariance of magnetic susceptibility when rotating a tight-binding Hamiltonian
We know the magnetic susceptibility for a non-interacting tight-binding model has the Lindhardt form, for which I express as product of matsubara Green's functions
$$\chi^{(0)}(q,\omega)=-\beta\sum_{k,...
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How to create the supercell to simulate a disordered solid solution?
I am trying to simulate the DOS of a disordered semiconductor (Cd0.5Zn0.5S), my plan is to get the .cif file of CdS first, and build a supercell, then I should ...
- 1,915
3
votes
2
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What happens to the position coordinates of the nearest neighbors in supercell studies?
Can anyone tell what happens to the position coordinates of the nearest neighbors when we choose to study supercell of the same material. That remains intact or any changes will be there?
For example ...
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4
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1
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Is there any useful application to estimating the expectation value for an Ising model without magnetic field?
In the same line of thoughts as this post, I am trying to understand better in which cases quantum computers could be useful to simulate materials under some constraints on what the quantum computer ...
8
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Are there interesting applications of estimating the energy for generalizations of the Heisenberg model?
I consider that $H$ is a Hamiltonian describing a quantum system of $n$ spin-1/2 particles (or qubits). I assume it can be written as (the $\alpha_k^i$ are real coefficients):
$$\tag{1}H=\sum_{i=1}^3 ...
5
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2
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What's the completeness relation of Bloch band?
Bloch's theorem can be stated as:
$$
|\Psi_{n\vec{k}}\rangle=e^{i\vec{k}\cdot\vec{r}}|u_{n\vec{k}}(\vec{r})\rangle \tag{1}
$$
where $|\Psi_{n\vec{k}}\rangle$ is the solution of single electron ...
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About the mechanism of opening of the band gap in topological insulator with the inclusion of SOC [closed]
When we work on the topological insulator (protected by time reversal symmetry ), it is often said that the SOC is the main ingredient because it is a way to open a gap when the band inversion present....
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The polarization lattice of a non-polar one dimensional chain [closed]
I have been trying to understand the concept of dielectric polarization in material science mostly by following Nicola Spaldin's lecture notes
I am confused by the claim that the polarization of a non-...
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What are differences between Mott and Anderson transitions?
Can anyone please explain the differences between Anderson and Mott insulator-metal transition? I found some information in the book named "The_Physics_of_Amorphous_Solids".
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How to map high symmetry points from primitive cell to conventional cell?
We usually plot electronic bands with the help of high symmetry points of the irreducible zone of primitive cell of particular material. But if we want to plot bands with conventional cell, we have to ...
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How to get a Wannier function for a tight-binding model numerically? [closed]
I have a question about construction of a Wannier function for a tight-binding model. Let's say we consider the tight-binding model of a 1D chain with two atoms (site A and B in a unit cell). In k-...
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What prevents us from designing material or catalysts to meet the custom requirements? [closed]
From the perspective of physics, everything is made of atoms, ions, electrons, etc. Since we know the basic interaction between elementary particles, it might be possible to design customized ...
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Can deformation potential theory be applied to 2D and 1D systems?
I was pointed towards the use of the Deformation Potential (DP) theory to calculate the electron relaxation time in a previous question.
However, I still have a doubt regarding its applicability to 2D ...
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Why is there a deviation between the experimentally calculated values and theoretical done by DFT calculation? [duplicate]
If there was a deviation between the experimentally calculated values and theoretical determination done by DFT calculation, then what is the reason?
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About LaCrO3 space group stability
I found two space groups of $\ce{LaCrO3}$ material Pnma and Pm-3m. If someone is familiar with this material, please help to understand which phase is more stable. what are the factors that determine ...
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2
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Why the band structure of a slab is not smooth?
I am trying to calculate the band structure of a TiO2-Rutile slab, but the result I got is not very smooth, and the result shows it is an indirect gap material, but the bulk phase of TiO2-Rutile is a ...
- 1,915
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Do the VBM and CBM have to be on the high symmetry point? [duplicate]
I am trying to generate the band structure of a slab, a lot of tutorials tell me that I need to generate the high symmetry K point path, but I am wondering that if the VBM and CBM have to be on the ...
- 1,915
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How to numerically calculate quantum state distance using quantum metric?
In Ran Cheng's review of the quantum geometric tensor, eq. (11) gives the tensor as:
$$
Q_{\mu\nu}=\sum_{n\neq 0}\frac{\langle\phi_0|\partial_\mu H|\phi_n\rangle\langle\phi_n|\partial_\nu H|\phi_0\...
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3
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How does a beginner condensed matter theorist working on real materials, get up to speed?
I asked this on Physics.SE and got recommended here.
More precisely, as a condensed matter theory PhD student, I am often overwhelmed by the wide variety of chemical formulas that experimentalists ...
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What software can I use for gas adsorption calculations?
We are from a new research group working on matter modelling. Currently our work has focused mainly on classical Molecular Dynamics (MD), Lattice Dynamics (LD) and ab-initio methods. For these, we ...
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1
answer
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Kramer's Degeneracy and Antiferromagnetism
How can one understand the concept of Kramer's Degeneracy for an antiferromagnetic system where spin-up and spin-down bands overlap due to net zero magnetic moment?
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How to identify localized surface states in the band structure
After calculating the band diagram of a structure, is there a way to identify localized surface states?
I am working with Si nanowires with different cross sections. I want to determine the band gap ...
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1
answer
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Evaluating Seebeck coefficient using DFT
I am working with semiconductor materials using the SIESTA DFT package. I have tried the BoltzTraP2 software interface with SIESTA, however the results (Seebeck coefficient of MgO and Si) did not ...
- 2,583
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What is signified by the properties of the electronic band structure?
When considering the band structure of two materials or two structures along a specific k path, what exactly is meant by the gradient and the distance between band lines?
Does this show any ...
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Constructing the symmetry operator from k.p Hamiltonian [closed]
I have a question regarding to how to construct an operator from k.p Hamiltonian. Maybe there are some problems in my understanding, I hope you can point me out and correct my description if I made ...
- 2,763
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votes
1
answer
71
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Imaginary time dependent operators: (anti)commutation relations
If I know trivial (anti)commutation relation for some operators (let's say Fermi operators), I can only use it if they are in the same moment of time. If I have their time dependence and they don't ...
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6
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1
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How to formulate the second quantization of Dzyaloshinskii-Moriya interaction?
The Dzyaloshinskii-Moriya interaction (DMI) existing in the interface of the ferromagnetic insulator and the metal with strong spin-orbit coupling (SOC) is shown below.
Mathematically, it can be ...
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votes
1
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Hubbard model SU(2) symmetry: manifest invariance
Could someone explain, is it possible to make Hubbard Hamiltonian manifestly SU(2) invariant? I know about the interaction term, but how would kinetic (hopping effect) term have to look like?
Here I'm ...
- 161
6
votes
1
answer
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Confusions in interpreting Dirac strings (wormholes) in Haldane's Hilbert space picture ft. two tori joined by strings at gapless points
I had a question about Haldane's wormhole interpretation (picture below). I believe he first proposed it in his paper Berry Curvature on the Fermi Surface: Anomalous Hall Effect as a Topological Fermi-...
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6
votes
1
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Help with definitions in k-space twisted bilayer graphene model
I am trying to numerically do calculations using Eq. 8 of MacDonald's simple model for twisted Bilayer graphene. I only want to calculate the Berry phase. However, I don't think I have my definitions ...
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Example of 2D k-space models allowing interband transitions after a closed-loop trajectory? [closed]
I have been mainly exposed to 2D momentum-space condensed matter models in the context of Berry-related topology. I now want to study models where, if I take a closed loop in momentum space, I will ...
- 2,131
6
votes
2
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891
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POSCAR data file for a 2D system
I would like to understand how to calculate the band structure of the Graphene monolayer system using DFT. I am using VASP for material simulation. My question is how to write the crystal structure ...
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The quantum spin Hall phase with Z2 = 0? [closed]
I used first principle calculations to study the thin film model. An obvious crossing was shown to appear at the gamma point when the edge state was calculated, which was originally predicted to be ...
- 2,763
11
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1
answer
239
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How to use wavefunctions/density to determine which orbitals lead to edge states?
I have a large matrix for a 1D zigzag edge model of an otherwise $3\times 3$ tight-binding Hamiltonian (3 basis functions, each corresponding to an atomic orbital), involving the variable $k_x$. The ...
- 2,131
9
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1
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Help with translating Hamiltonian into matrix
Eq. 19 in this paper gives the following Hamiltonian:
$\sigma_a, \tau_a, \eta_a$ are respectively the spin, sublattice pseudospin and valley pseudospin respectively.
Normally, I would have chosen a ...
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Z2 topological index: Is this unconventional formula summed over just filled bands, or all bands? [closed]
The $\mathbb{Z}_2$ topological index is usually defined in terms of the Pfaffian of the overlap matrix, as defined by eq. 4 of Kane and Mele's paper:
$$
P(k)=\text{Pf}[\langle u_i(k) | \Theta | u_j(k) ...
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7
votes
1
answer
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Help with Definitions in Numerical Calculation of Multiband Berry Phase
In the third chapter of Vanderbilt's book, they discuss the so-called multiband parallel transport and provide a scheme for numerical calculations that is similar to the single band case (where the ...
- 2,131
12
votes
1
answer
243
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How to numerically solve real-space 1D time-independent Schrodinger equation using 2D momentum-space Hamiltonian?
Consider the usual simple 2-level graphene Hamiltonian with mass in momentum-space where:
$$
H(k,V)=-t \sum_{\delta} [\cos(k\cdot\delta)\sigma_x-\sin(k\cdot\delta)\sigma_y+V\sigma_z],
$$
where $t$ is ...
- 2,131
8
votes
1
answer
100
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Help with understanding topologically-protected edge states in domain wall systems
Let's say that I have a simple domain wall system for the following Hamiltonian with added on-site potential $M(x)$:
$$\tag{1}
H(k,M)=-t \sum_{\delta} [\cos(k\cdot\delta)\sigma_x-\sin(k\cdot\delta)\...
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