From: High-pressure study of thermodynamic parameters of diamond-type structured crystals using interatomic Morse potentials
Crystal
c11
c12
c13
c33
Si (present)
1.85
0.64
0.55
2.13
Si (expt.)
1.77
0.41
0.61
1.54
Ge (present)
1.46
0.57
0.46
1.63
Ge (expt.)
1.35
0.52