Thanks for your reply! So as we agree:

The known the stiffness tensor from MP is

C=[97 -20 -20 0 0 0

-20 97 -20 0 0 0

-20 -20 97 0 0 0

0 0 0 102 0 0

0 0 0 0 102 0

0 0 0 0 0 102]

If we let the first strain tensor be

epsilon_1=[ 0.004999903894075897, 0.0, 0.0 ], [ 0.0, -1.1102230246251565E-16, 0.0 ], [ 0.0, 0.0, -1.1102230246251565E-16 ]

we obtain the first stress tensor

sigma_1=C*epsilon_1=[0.485, 0, 0 ], [ 0, -0.1, 0 ], [ 0, 0, -0.1 ],

which is the same with [ 0.485835569, 0.0, -0.0 ], [ -0.0, -0.100418809, -0.0 ], [ -0.0, -0.0, -0.100418809 ]

But if we let the second strain tensor be

epsilon_2=[ -1.1102230246251565E-16, 0.0, 0.0 ], [ 0.0, -1.1102230246251565E-16, 0.005000051366872475 ], [ 0.0, 0.005000051366872475, -8.041918347911903E-8 ]

we obtain the second stress tensor

sigma_2=C*epsilon_2=[0, 0, 0 ], [ 0, 0, 5.1 ], [ 0, 5.1 , 0 ]

which is different from [ -0.177069249, -0.0, -0.0 ], [ -0.0, -0.166530955, 1.024832653 ], [ -0.0, 1.024832653, -0.18702881500000001 ]

Could you please tell me the reason? Is the stiffness tensor provided by MP not correct OR I made some mistakes during the derivation process?