Hi @MilMou,
I agree it’s important to figure out what’s going on here. If it helps, here are the stress/strains we used to fit this specific elastic tensor:
cauchy_stresses = [
[ [ 0.485835569, 0.0, -0.0 ], [ -0.0, -0.100418809, -0.0 ], [ -0.0, -0.0, -0.100418809 ] ],
[ [ -0.177069249, -0.0, -0.0 ], [ -0.0, -0.166530955, 1.024832653 ], [ -0.0, 1.024832653, -0.18702881500000001 ] ],
[ [ -0.10041880899999997, 0.0, 0.0 ], [ 0.0, 0.4858355689999999, 0.0 ], [ 0.0, 0.0, -0.10041880899999997 ] ],
[ [ -0.10041880899999997, 0.0, 0.0 ], [ 0.0, -0.10041880899999997, 0.0 ], [ 0.0, 0.0, 0.4858355689999999 ] ],
[ [ -0.16653095499999998, 0.0, -1.0248326529999998 ], [ 0.0, -0.17706924899999998, 0.0 ], [ -1.0248326529999998, 0.0, -0.187028815 ] ],
[ [ -0.17706924899999998, 0.0, 0.0 ], [ 0.0, -0.16653095499999998, -1.0248326529999998 ], [ 0.0, -1.0248326529999998, -0.187028815 ] ],
[ [ -0.16653095499999998, 0.0, 1.0248326529999998 ], [ 0.0, -0.17706924899999998, 0.0 ], [ 1.0248326529999998, 0.0, -0.187028815 ] ],
[ [ -0.187028815, -1.0248326529999998, 0.0 ], [ -1.0248326529999998, -0.16653095499999998, 0.0 ], [ 0.0, 0.0, -0.17706924899999998 ] ],
[ [ -0.187028815, 1.0248326529999998, 0.0 ], [ 1.0248326529999998, -0.16653095499999998, 0.0 ], [ 0.0, 0.0, -0.17706924899999998 ] ]
]
strains = [
[ [ 0.004999903894075897, 0.0, 0.0 ], [ 0.0, -1.1102230246251565E-16, 0.0 ], [ 0.0, 0.0, -1.1102230246251565E-16 ] ],
[ [ -1.1102230246251565E-16, 0.0, 0.0 ], [ 0.0, -1.1102230246251565E-16, 0.005000051366872475 ], [ 0.0, 0.005000051366872475, -8.041918347911903E-8 ] ],
[ [ -1.1102230246251563E-16, 0.0, 0.0 ], [ 0.0, 0.004999903894075896, 0.0 ], [ 0.0, 0.0, -1.1102230246251563E-16 ] ],
[ [ -1.1102230246251563E-16, 0.0, 0.0 ], [ 0.0, -1.1102230246251563E-16, 0.0 ], [ 0.0, 0.0, 0.004999903894075896 ] ],
[ [ -1.1102230246251563E-16, 0.0, -0.005000051366872474 ], [ 0.0, -1.1102230246251563E-16, 0.0 ], [ -0.005000051366872474, 0.0, -8.041918347911901E-8 ] ],
[ [ -1.1102230246251563E-16, 0.0, 0.0 ], [ 0.0, -1.1102230246251563E-16, -0.005000051366872474 ], [ 0.0, -0.005000051366872474, -8.041918347911901E-8 ] ],
[ [ -1.1102230246251563E-16, 0.0, 0.005000051366872474 ], [ 0.0, -1.1102230246251563E-16, 0.0 ], [ 0.005000051366872474, 0.0, -8.041918347911901E-8 ] ],
[ [ -8.041918347911901E-8, -0.005000051366872474, 0.0 ], [ -0.005000051366872474, -1.1102230246251563E-16, 0.0 ], [ 0.0, 0.0, -1.1102230246251563E-16 ] ],
[ [ -8.041918347911901E-8, 0.005000051366872474, 0.0 ], [ 0.005000051366872474, -1.1102230246251563E-16, 0.0 ], [ 0.0, 0.0, -1.1102230246251563E-16 ] ]
]
And this is for structure:
Full Formula (Ge1 Pb1 O3)
Reduced Formula: GePbO3
abc : 3.893560 3.893560 3.893560
angles: 90.000000 90.000000 90.000000
Sites (5)
# SP a b c magmom
--- ---- ---- ---- --- --------
0 Ge 0.5 0.5 0.5 -0
1 Pb 0 0 0 -0
2 O -0 0.5 0.5 0
3 O 0.5 0.5 0 -0
4 O 0.5 -0 0.5 -0
Best,
Matt