Dear Developers,

In the 1987 IEEE Standard on Piezoelectricity, section 3.2, the signs of the Cartesian axes are related to the signs of certain dielectric constants. For example:

3.2.1 The Triclinic System

…

The +Z and +X axes are chosen so that d33 and d11 are positive.

…

3.2.4 The Tetragonal System

…

With classes 4 and 4mm the +Z axis is chosen so that d33 is positive and +X and + Y are parallel to a to form a righthanded system. With class , +Z is chosen so that d31 is positive and +X and +Y are parallel to a to form a right-handed

system. In classes 2m and 422 the +Z axis (parallel to c) is chosen arbitrarily. In class 2m the +X and +Y axes are

chosen parallel to the twofold axes (which are not parallel to the a axis for the space groups listed) such that d36 is

positive.

…

For trigonal and hexagonal crystals, the rules are even more complex and constitute an entire table…

I am not an expert on piezoelectricity, but it seems to me that you can’t know this *a priori* without doing a calculation. Does this mean that get_ieee_rotation is consistent with the IEEE standard only up to the choice of axis sense?

Cheers, ilia