Questions tagged [condensed-matter]
For all matters related to condensed matter physics.
108
questions
10
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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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17
votes
2
answers
581
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Software for solving quantum systems in 1D and 2D
I'm looking to solve quantum system in 1D and 2D consisting of a large number of sites.
What are the pros and cons of each package, and which package is more suitable for what type of calculations?
...
- 2,593
9
votes
1
answer
211
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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 ...
- 2,593
10
votes
1
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125
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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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14
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1
answer
139
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What are the physical consequences of adding a constant to the diagonal of the effective Hamiltonian of monolayer materials?
Effective Hamiltonians modeling many-layered materials are often tuned using some sort of bias voltage. For instance, in a $4\times 4$ Hamiltonian matrix to describe biased bilayer graphene using some ...
- 2,131
5
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0
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271
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Why does numerical computation of Berry curvature give me a correct Berry phase when it is supposed to diverge? [closed]
I implemented the standard numerical algorithm for calculating the Berry curvature in MATLAB. For a given 2D system, I can visualize the Berry curvature over parameter space. If I sum the Berry ...
- 31.6k
6
votes
0
answers
94
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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 ...
- 1,708
7
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0
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192
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How to fix gauge in Quantum ESPRESSO? [closed]
I am trying to use Quantum ESPRESSO to manually calculate the Berry phase using the Berry connection, due to evolution along a closed loop in k-space. I want to do this manually instead of using ...
- 31.6k
6
votes
0
answers
68
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Value of density of state effective mass and transport effective mass to calculate conductivity [closed]
How can density of state effective mass and transport effective mass can be defined to calculate conductivity for a cubic system with parabolic but anisotropic dispersion relation? What will be the ...
- 31.6k
12
votes
0
answers
107
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First principles calculations beyond s-wave BCS superconductors [closed]
Conventional superconductors are often modelled using Bardeen-Cooper-Schrieffer (BCS) theory with an s-wave order parameter, but not all superconductors describable with BCS theory have an s-wave ...
- 31.6k
5
votes
0
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50
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What's the difference between dynamic and static strain aging? [closed]
I do understand how static strain aging occurs and why the yield point comes back if ample time is allotted after a loading and unloading cycles primarily due to diffusion of substitutional and ...
- 31.6k
4
votes
1
answer
122
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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 ...
- 31.6k
6
votes
1
answer
74
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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 ...
- 31.6k
30
votes
0
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378
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Where/when did the fields of Operations Research and Spin Physics or Molecular Dynamics begin to cross-pollinate?
Operations Research is a field of mathematics in which optimal or near-optimal solutions are sought for complicated problems.
In the modeling of materials, we often optimize Ising models, in which the ...
- 14.7k
6
votes
1
answer
57
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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-...
- 2,131
6
votes
1
answer
123
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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 ...
- 2,131
2
votes
0
answers
104
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Materials Modeling in Industry [closed]
This question is primarily targeted to individuals who are working in industries and in the field of materials modeling.
[Be ambiguous wherever required]
(i) Please explain your role briefly
(ii) ...
- 14.7k
6
votes
0
answers
40
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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
11
votes
1
answer
251
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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 ...
- 2,959
7
votes
0
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43
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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 ...
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6
votes
2
answers
996
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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 ...
- 14.7k
5
votes
0
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99
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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:
$$
P(k)=\text{Pf}[\langle u_i(k) | \Theta | u_j(k) ...
- 31.6k
9
votes
1
answer
284
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Help with translating Hamiltonian into matrix
Eq. 19 in this paper gives the following Hamiltonian:
$\sigma_a, \tau_a, \eta_a$ are respectively the spin, sublattice pseudospin and valley pseudospin respectively.
Normally, I would have chosen a ...
- 31.6k
16
votes
3
answers
1k
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What are some codes available for Dynamical Mean Field Theory (DMFT)?
One particularly field of matter modeling is that of strongly correlated materials, heavy-fermion compounds with partially filled 4f or 5f orbitals. In brief, these are materials whose complex ...
- 14.7k
7
votes
1
answer
227
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Help with Definitions in Numerical Calculation of Multiband Berry Phase
In the third chapter of Vanderbilt's book, they discuss the so-called multiband parallel transport and provide a scheme for numerical calculations that is similar to the single band case (where the ...
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1
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257
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How to numerically solve real-space 1D time-independent Schrodinger equation using 2D momentum-space Hamiltonian?
Consider the usual simple 2-level graphene Hamiltonian with mass in momentum-space where:
$$
H(k,V)=-t \sum_{\delta} [\cos(k\cdot\delta)\sigma_x-\sin(k\cdot\delta)\sigma_y+V\sigma_z],
$$
where $t$ is ...
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10
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1
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286
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How can I calculate the J value in an antiferromagnetic material?
I am new to DFT, especially in doing DFT for magnetic materials. I recently came across this paper which indicated the calculation of the J value in the case of antiferromagentic materials as per the ...
- 31.6k
15
votes
3
answers
3k
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What does “strongly correlated” mean?
For quantum many body problem, there is a common terminology “strong correlated systems” that appears in different context. However, it seems that the definition of it is ambiguous and sometimes ...
- 14.7k
12
votes
2
answers
744
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How can we say that the KS equation is describing a noninteracting many-electron system?
Based on HK's two theorems, the density functional theory was built. Because one can't find the universal energy functional $F_{HK}[n(r)]$, Kohn and Sham further proposed the Kohn-Sham ansatz: mapping ...
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6
votes
1
answer
66
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Example of a standard/archetypal/simple 4-band un-gapped condensed matter model with analytic results?
I am looking to study Berry phase-like phenomena in an un-gapped material model. However, I am having trouble finding a widely-used 4-band model with analytic expressions for wavefunctions and ...
- 31.6k
17
votes
1
answer
4k
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How to understand the time-reversal symmetry in graphene?
A lot of references say that the Dirac cone in graphene is protected by inversion and time-reversal symmetries. How can one understand this statement? How can one show explicitly that the gapless ...
- 14.7k
10
votes
1
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326
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What's the past and future of 2D materials since graphene?
Since the discovery of graphene in 2004, two-dimensional (2D) materials have been a hot topic in the community of condensed matter physics, which can be considered as the candidate for next-generation ...
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6
votes
1
answer
280
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Thermo-calc: Calculate precipitation driving force by parallel tangent construction
I want to calculate the difference in Gibbs free energies between a
Zr-Cu-Al liquid (composition - Zr 65 Cu 27.5 Al 7.5 at%) and the CuZr2
solid phase as a function of temperature (300 - 1000 K). In ...
- 1,708
11
votes
1
answer
397
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How to start with structural defects in monolayer?
First of all, thank you for your help!
You are so helpful every time.
I would like to calculate the influence of the structural defects on the electronic structure in the HfS2 monolayer. With VESTA ...
- 14.7k
14
votes
1
answer
795
views
When do we abandon ab initio methods?
This question is related to (and was originally asked in) another post about "quantum protectorates" I made here.
Ab initio methods are nice because they directly solve a sort of "...
- 31.6k
5
votes
0
answers
46
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A doubt about extended dislocation [closed]
I wonder why this phenomenon occurs:
"Unlike unextended screw dislocations, the extended screw dislocations
define a specific slip plane, the {111} plane of the fault and it
will be constrained ...
- 31.6k
3
votes
0
answers
55
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Doubt in Raoultian and Henrian Standard State [closed]
$Si(liq)=Si_\text{(1 wt% Fe)}$
Can you describe what is going on here?All that they ask for is change in Gibbs free energy for the process.I am completely unable to figure why this particular model is ...
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votes
1
answer
75
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Where is this extra plane coming from?
Why are there solid lines drawn connecting the solid circles after twinning has taken place? Ideally, that explains a real plane, isn't it? But why are we going to get a plane out of nothing if we ...
- 651
8
votes
1
answer
81
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How to predict new Half Metallic materials with higher degree of spin polarization?
Using DFT calculations, how one can predict the new half metallic materials with higher degree of spin polarization. I want to know the steps which have to be followed in prediction of new materials. ...
- 14.7k
11
votes
2
answers
2k
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How to choose pseudopotential for DFT calculations in Quantum ESPRESSO?
I am a beginner and newly started running DFT calculations to find out the electronic band structure of certain materials in Quantum ESPRESSO. But we have to select the pseudopotential for running the ...
- 3,188
12
votes
3
answers
1k
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External magnetic field in VASP?
I have never found any tags or documentation regarding external magnetic field in VASP but in different well known published articles$^1$, the implementation of the external magnetic field by VASP has ...
- 10.8k
8
votes
0
answers
55
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Symmetry of glide planes [closed]
I am trying to understand the symmetry elements of space group number 194 (P$6_3$/mmc), which is hexagonal and has 24 symmetry operations.
In the table of symmetry operations it says that it has three ...
- 31.6k
8
votes
1
answer
756
views
How to perform virtual crystal approximation calculations in VASP?
Can someone share appropriate tags and methods to perform virtual crystal approximation calculations in VASP?
- 10.8k
12
votes
2
answers
127
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What are real examples where fractals were used in Matter Modeling?
A fractal is, accordingly Oxford English Dictionary:
A curve or geometric figure, each part of which has the same statistical character as the whole. Fractals are useful in modeling structures (such ...
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3
votes
1
answer
80
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How to simulate a furnace computationally
I am trying to synthesize MoSe$_2$ crystals in a furnace with two temperature zones.
The problem is that the oven is not very wide, so the temperature of the hottest zone influences the temperature of ...
- 31.6k
11
votes
1
answer
996
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Real space projection vs reciprocal space projection in DFT calculations
When doing VASP calculations for large cells, we get a warning:
"You have a (more or less) 'large supercell' and for larger cells it
might be more efficient to use real space projection ...
- 31.6k
21
votes
2
answers
803
views
Is there a list of all universality classes for phase transitions with examples of each?
I've often had this problem: I have a model that has a phase transition in it, but I don't know what universality class it falls into or what the universality class is called.
Is there anywhere on ...
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1
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89
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Property related with Berry curvature: $\Omega_{n,\mu\nu}=-\Omega_{n,\nu\mu}$
I read in David Vanderbilt's book named "Berry Phases in Electronic Structure Theory - Electric Polarization, Orbital Magnetization and Topological Insulators" the definition of Berry ...
- 4,536
19
votes
1
answer
1k
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Difference between potential energy, free energy and Coulomb energy in solid state physics
I often encounter terms such as (Helmholtz, Gibbs) free energy, potential energy and total energy when describing the energy of a physical system at atomic level. Sometimes I stumble upon Coulomb ...
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20
votes
1
answer
156
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What class of materials are closest to realizing the tunable coupling Hamiltonian?
From a physics point of view, there is an effective (approximation to second-order coupling Jaynes-Cummings) Hamiltonian of the form [1]
\begin{equation}
H=\sum_j\omega_j(t)\sigma_j^z+\sum_{\langle i,...
- 31.6k