Questions tagged [symmetry]
Questions relating to symmetries and symmetry groups encountered in materials modeling.
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questions
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How to build a nanocluster?
What are the software tools (if possible open source) or methods we can use for constructing a nanocluster, most preferably with high symmetry such as icosahedron, octahedron, cuboctahedron etc. ?
8
votes
2answers
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What will break the time-reversal symmetry?
Specifically, I am interested in the time-reversal symmetry $(\mathcal{T})$ in quantum mechanics. The $\mathcal{T}$ is considered as an anti-unitary operator, namely:
$$\mathcal{T}\psi(\vec{r},t)=\psi^...
10
votes
3answers
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Rotation of crystal structure to match another structure of the same compound/polymorph
Say, I have two crystal structures of a particular organic molecule, the crystal structures are basically identical, apart from a rotation and redefinition of the lattice vectors/angles, a simple ...
9
votes
1answer
119 views
PT-symmetry leading to spin-degenerate band structures
I am trying to understand the fundamental physics of a kind of problem. I will introduce a specific example and then list some of the broader qualms I hold. I have observed many band structures, be it ...
11
votes
1answer
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Nematicity in superconductors
It seems to me that the definition of "nematic phase" is quite chamaleonic.
Quoting from its first definition [Nature 393, 550 (1998)] for a 2-dimensional square lattice "The nematic ...
8
votes
1answer
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Topological order in Weyl Semimetal
Is the topological phase in a Weyl semimetal is intrinsic or symmetry protected? How can we realize that?
If symmetry protected, which symmetry protects the topological phase of non-centrosymmetric ...
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0answers
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Why linear response is absent in a non-centrosymmetric system with time reversal symmetry?
In this paper, it is mentioned that a non-centrosymmetric system with time-reversal symmetry doesn't have a linear response. It is actually a consequence of the Onsager reciprocal theorem.
But I didn'...
9
votes
1answer
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How to analyze the band symmetry with Quantum ESPRESSO?
This question is related to this paper: J. Phys. Chem. Lett. 2017, 8, 13, 2999–3007
The above figure shows symmetry analysis for the band structure. The author writes:
The band symmetry and parity ...
6
votes
1answer
79 views
Is there a difference in performance when the symmetry is specified via ibrav in Quantum ESPRESSO?
I have been using cif2cell for converting CIF files into quantum ESPRESSO input files. But cif2cell always keeps the ibrav value to be zero and indicates the CELL_PARAMETERS. As per the quantum ...
13
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1answer
107 views
What does it mean to assign group operations to distinct sets for space groups?
I am trying to understand space groups in crystallography. In International tables for crystallography, for a nonsymmorphic space group, they list some symmetry operations. 8 of them are listed under ...
10
votes
1answer
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Partial density of states in random solid solutions
This question comes as a follow-up to https://mattermodeling.stackexchange.com/a/2214/116; nonetheless, it is relevant on its own as well.
To designate a particular crystal structure to a random ...
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1answer
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Why does mcsqs change the space group of generated SQS?
I made a binary special quasi-random structure (SQS) using mcsqs (distributed as part of the ...
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0answers
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How to classify ionic and covalent excited-states?
In spectroscopy it is common to describe excited-states as ionic or covalent.
I understand the concept on a toy model e.g. $\ce{H2}$ with a minimal basis set
$$
\Phi_0 = [\chi_A(1) + \chi_B(1)][\...
11
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2answers
238 views
Effect of ISYM tag on Partial Density of States (VASP version < 6)
This is from the entry for LORBIT in the VASP Wiki.
For LORBIT >= 11 and ...
8
votes
1answer
140 views
Inversion symmetry in 2D materials
Transition metal dichalcogenides (TMDs) are composed of three atomic planes and often two atomic species: a metal and two chalcogens. The honeycomb, hexagonal lattice has three fold symmetry and can ...
10
votes
1answer
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Get fractional coordinates from special Wyckoff positions
I'm trying to get the fractional coordinates for Mo and S, for MoS$_2$-2H, where 2H means the phase. MoS$_2$-2H is a bilayer, in which each layer is separated from each other by Van der Waals forces. ...
9
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0answers
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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 ...
15
votes
4answers
287 views
How is group theory used to deduce which of these integrals are equal to 0?
The number of all two-electron integrals:
$$
\tag{1}
\langle \phi_1 \phi_2|\phi_3\phi_4 \rangle = \int d^3\mathbf r' \int d^3\mathbf r'' \, \phi_1(\mathbf r'') \, \phi_2(\mathbf r') \frac{1}{|\mathbf ...
16
votes
2answers
491 views
How to deduce phase transitions from a phonon calculation?
I came across the concept of using phonons to establish a material's dynamical stability, based on whether or not imaginary frequencies are present in its phonon band structure.
What I am struggling ...
16
votes
1answer
938 views
How to understand 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 ...
12
votes
1answer
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Dealing with symmetry of ordered primitive cell during DFT structure relaxation
I have a large disordered cubic structure that I would like to do AIMD on to look at cation diffusion. I found the primitive cell and then ordered it to create several configurations. I will then ...
18
votes
1answer
985 views
Is the number of possible Bravais lattices a mathematical fact?
Almost anyone that has taken a Solid State Physics course will know, that any 3D crystal must be in one of the 14 Bravais lattices due to symmetry operations and space filling.
In 2015, a paper was ...
15
votes
1answer
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conceptual problem about the energy band along the High symmetry point in the Brillouin zone
When we calculate the band structure of certain material, we only have to calculate the value along the high symmetry point which enclose the Irreducible Brillouin Zone. Why the information lie in the ...
10
votes
1answer
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What is the difference between U(1) and O(2) symmetry?
To my understanding, they both refer to circular symmetry. I know U(1) is the complex plane, and I think O(2) is real numbers. I have seen them used more or less interchangably, but is there actually ...
