Hello!
Please help with the following. I got the result of calculating the elastic
constants of LKBO (orthorhombic, P212121, Space group 19) using thermo_pw
(what='scf_elastic_constants', 'elastic algorithm = 'advanced'). The
calculation was done, but I found 2 problems:
1) the resulting matrix is asymmetric: 0.1310416661E+04
0.5760227795E+03 0.3377111274E+03 0 0 0 0.5721874370E+03
0.7221687324E+03 0.3757178266E+03 0 0 0 0.3222687958E+03
0.3774439747E+03 0.1122193660E+04 0 0 0 0
0 0 0.2688418051E+03 0 0
0 0 0 0
0.2782351915E+03 0 0 0 0 0 0
0.2810735472E+03
2) the data do not correspond to experimental results.
Some explanations:I noticed that in half SCF calculations, QE identified the
symmetry of the crystal as monoclinic (bravais-lattice index = 12 or -12), and
in the others - bravais-lattice index = 8 (orthorhombic). At the start, we
received the following symmetry information:
Bravais lattice 8 simple orthorhombic Point
group number 8 / 38 D_2 (222)
The coset representatives of the space group with the standard order
of operations are:
Fractional translations in crystal coordinates
PGS Fract. transl. (all) Fract. transl. (no shift) SGS
E 1 -0.0000 -0.0000 -0.0000 0.0000 0.0000 0.0000 E 1
2z 2 -0.5000 -0.0000 0.5000 0.0000 0.0000 0.5000 2z1 65
2x 4 0.5000 -0.5000 -0.0000 0.5000 0.0000 0.0000 2x1 67
2y 3 -0.0000 0.5000 -0.5000 0.0000 0.5000 0.0000 2y1 66
PGS = Point group symmetry, SGS = space group symmetry (no shift)
means the part of the fractional translation that cannot be removed by an
origin shift
Fractional translation shift and origin shift in crystal coordinates
PGS FT shift &Origin shift SGS
E 1 -0.0000 -0.0000 -0.0000 0.0000 0.0000 0.0000 E 1
2z 2 -0.5000 0.0000 0.0000 -0.2500 0.0000 0.0000 2z1 65
2x 4 0.0000 -0.5000 0.0000 0.0000 -0.2500 0.0000 2x1 67
2y 3 0.0000 0.0000 -0.5000 0.0000 0.0000 -0.2500 2y1 66
The origin shift gives the point of application of the symmetry
Subtract this vector from all atomic coordinates to have this symmetry
centered at the origin
Space group number 19
Space group P2_12_12_1 (group number 19).
The Laue class is D_2h (mmm)
In this class the elastic tensor is
( c11 c12 c13 . . . ) ( c12 c22 c23 . . . )
( c13 c23 c33 . . . ) ( . . . c44 . . ) ( .
. . . c55 . ) ( . . . . . c66 )
It requires all six strains. for a total of 24 scf calculations
In the input file, atomic coordinates were used, the relaxation of which was
carried out without considering symmetry (ibrav=0). JTH-LDA data sets were used
(ecutwfc = 81 Ry, occupations = 'tetrahedra_opt', conv_thr = 1.D-8).
I would be grateful for any ideas to improve the calculation results.
Thanks,Oleksandr
_______________________________________________
The Quantum ESPRESSO community stands by the Ukrainian
people and expresses its concerns about the devastating
effects that the Russian military offensive has on their
country and on the free and peaceful scientific, cultural,
and economic cooperation amongst peoples
_______________________________________________
Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
users mailing list [email protected]
https://lists.quantum-espresso.org/mailman/listinfo/users
