I’ve noticed that the MP piezoelectric calculation for wurtzite AlN, mp-661, doesn’t appear to match the values listed in de Jong et al.'s Scientific Data paper. The paper says " As an example, for the wurtzite-compound AlN, we calculate e 33=1.46 C/ m 2 and e 31=−0.58 C/ m 2 which is within 10% of the values reported elsewhere, obtained using GGA as well, but with a different implementation of DFPT and slightly different convergence parameters". However, here’s the MP piezoelectric tensor:
I tried calculating the piezoelectric properties in VASP the old-fashioned way with LCALCEPS = .TRUE., and got (electronic + ionic)
0.0 0.0 0.0 0.0 0.0 -0.30
0.0 0.0 0.0 0.0 -0.28 0.0
-0.58 -0.58 1.46 0.0 0.0 0.0
which at least agrees with de Jong et al. for e31 and e33. (According to the VASP wiki the sign of this piezoelectric tensor is wrong for VASP 5.4.4 and older, but this seems to affect everyone equally) Are the MP values transformed to a different set of axes, or something?