For the two ways to set up a hcp structure according to textbooks, EXCITING reports differently in terms of the existence of inversion. The first way is:
AVEC
0.5 -0.866 0.0
0.5 0.866 0.0
0.0 0.000 1.0
ATOMS
1/3 2/3 1/4
2/3 1/3 3/4
The second way is:
AVEC
1.0 0.000 0.0
-0.5 0.866 0.0
0.0 0.000 1.0
ATOMS
0.0 0.0 0.0
1/3 2/3 1/2
Exciting reports that both structures have 12 Bravais lattice symmetries, 6 crystal symmetries, but the first one has inversion and second one no inversion. I am wondering why there is such a difference and whether it will influence calculations.
with best regards!
zhangyg
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The difference won't influence the calculations. The code searches all possible symmetry centers for the one with the largest number of symmetries. Since they both have 12, the code just picks the first one. Currently, there is no reason to select the one with inversion (the other has improper rotations). In the future I'll probably implement real Hamiltonians for these cases: currently the Hamiltonian is always complex.
Best wishes,
Kay.
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Dear Kay:
For the two ways to set up a hcp structure according to textbooks, EXCITING reports differently in terms of the existence of inversion. The first way is:
AVEC
0.5 -0.866 0.0
0.5 0.866 0.0
0.0 0.000 1.0
ATOMS
1/3 2/3 1/4
2/3 1/3 3/4
The second way is:
AVEC
1.0 0.000 0.0
-0.5 0.866 0.0
0.0 0.000 1.0
ATOMS
0.0 0.0 0.0
1/3 2/3 1/2
Exciting reports that both structures have 12 Bravais lattice symmetries, 6 crystal symmetries, but the first one has inversion and second one no inversion. I am wondering why there is such a difference and whether it will influence calculations.
with best regards!
zhangyg
The difference won't influence the calculations. The code searches all possible symmetry centers for the one with the largest number of symmetries. Since they both have 12, the code just picks the first one. Currently, there is no reason to select the one with inversion (the other has improper rotations). In the future I'll probably implement real Hamiltonians for these cases: currently the Hamiltonian is always complex.
Best wishes,
Kay.