Dear all,
I performed a vc-relax calculation using QE of an ice crystal (hexagonal lattice: ibrav=4). The result was=
CELL_PARAMETERS (alat= 14.77765829)
0.964571031 0.000000000 0.000000000
-0.482285515 0.835343016 0.000000000
0.000000000 0.000000000 0.908263535
My questions are:
1- How can I convert the values in this matrix to "a", "b", and "c" lattice parameters in bohr to further convert to angstroms? I watched a video showing how to obtain "a" and "c", but not "b" ("b" should be equal to "a", but I don't find a way to calculate it from the matrix result)...
2- Looking for tutorials on Youtube, I saw that each crystal family has a different way to convert the values. How can I know the specific calculation to perform in the conversion?
3- Are there any materials explaining the way to choose the conversion system?
Thanks a lot for your help!!!
Hi,
The matrix that you have is like
a 0 0
-a/2 sqrt(3) a /2 0
0 0 c
so just get "a" and directly from the matrix and for "b" multiply by 2 to (2,1) element or multiply by 2/sqrt(3) to (2,2) element, you will get the same result.
For unit conversion thing first of all you have to multiply the whole matrix by this "alat" thing and follow the above procedure.
For the conversion in to Angstrom just multiply with bohr radius (~0.52917).
Dear Abdul Ahad,
Thank you a lot for your answers and the time spent.
In this case, I multiply all the values in the matrix by alat value, getting:
14.25410109 0.0000000000 0.0000000000
-7.127050538 12.344413645 0.0000000000
0.000000000 0.0000000000 13.422008157
If I understand right, for hexagonal space group:
v1 = alat(1, 0, 0)
v2 = alat(-1/2 , sqrt(3)/2, 0)
v3 = alat(0, 0, c/a),
with v1 = "a", v2 = "b", and v3 = "c"
Thus, "a" = 14.25410109 (7.5546 A); "b" = [7.127050538 * 2] (7.5546 A); and "c" = 13.422008157 (7.1136 A).
Is that correct?
Yes, it is correct according to description of QE.
You can verify with the known systems.
Thank you
Hi José,
there is a fast way to do this without any calculation.
You can use the XCrysden software to open the QE inputs/output files. Then you can save the file in the XCrysden format. In this format, you can read all variables such as lattice vectors and coordinates in the rectangular coordinates format (Bohr and Angstrom).
Best regards
Raphael
Thank you Raphael Tromer
It is quite easier than calculate all the lattice vectors.
Best regards
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