C11=176,7 GPa which is greater than 0.
C44=78.0 GPa which is greater than 0.
C11-C12=54.3 GPa which is greater than 0.
C11+2*C12= 421,5 GPa which is also greater than 0.
These four evaluations are part of the Born stability condition which is met for this experimental values of fcc CU.