Questions tagged [symmetry]
Questions relating to symmetries and symmetry groups encountered in materials modeling.
28
questions
16
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2answers
524 views
What are good tools for visualizing glide planes and screw axes?
While there are a few tools for visualizing crystal structures, I'm particularly curious to know tools for visualizing space group symmetry, including:
screw axes
glide planes
I teach a class on ...
5
votes
0answers
25 views
Construct a parity operator in TRIM
I want to calculate the band parity at some TRIM in Brillouin zone. Parity was defined as the eigenvalue of the inversion operator. My question is how to construct the matrix representation of the ...
5
votes
1answer
69 views
How do I extract the wave function from a VASP calculation?
We can obtain a energy band structure of a crystal from a DFT calculation in Vasp. Each point in each band represents an energy eigenvalue with a corresponding wave function from the Schrödinger ...
5
votes
0answers
111 views
What's the information contained in a character table of a group? [closed]
This question has an answer on the Chemistry Stack Exchange: Understanding group theory easily and quickly.
Anyone wishing to add alternative or additional perspectives that aren't already covered in ...
11
votes
3answers
740 views
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
101 views
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^...
11
votes
3answers
121 views
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
128 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 ...
10
votes
1answer
164 views
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 ...
9
votes
1answer
103 views
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 ...
12
votes
1answer
131 views
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'...
10
votes
1answer
127 views
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 ...
5
votes
1answer
93 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 ...
12
votes
1answer
111 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 ...
9
votes
1answer
91 views
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 ...
9
votes
1answer
91 views
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 ...
6
votes
0answers
71 views
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
\begin{align}
\Phi_0 &= [\chi_A(1) + \...
11
votes
2answers
301 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
208 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 ...
9
votes
1answer
220 views
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. ...
8
votes
0answers
44 views
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
312 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
536 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
1k views
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 ...
11
votes
1answer
152 views
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
1k 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 ...
14
votes
1answer
145 views
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 ...
9
votes
1answer
217 views
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 ...
