Table 1.
The energy per formula unit and polarization for the non-polar H-NNO as well as 6 polar structures
| Structure | Space group | Energy (meV/f.u.) |
Polarization (μC/cm2) |
|---|---|---|---|
| Non-polar | P21/m (#11) | 0 | (0.0,0.0,0.0) |
| Polar 1 | P21 (#4) | −159 | (0.0,0.0,1.9) |
| Polar 2 | P1 (#1) | −50 | (−20.6, −5.4, 1.4) |
| Polar 3 | P1 (#1) | −145 | (−17.4, 14.8, 3.0) |
| Polar 4 | P1 (#1) | −68 | (−23.7, −7.0, 0.8) |
| Polar 5 | P1 (#1) | −140 | (−28.0, −26.5, −1.2) |
| Polar 6 | P1 (#1) | −165 | (−45.7, −12.9, 0.0) |
The italic symbols represent crystallographic space groups.
The non-polar structure is taken as the zero for both the energy and the polarization to define the branch choice. The polarization is reported as a vector in cartesian coordinates where the (110) direction (defined in an orthorhombic cell) - the epitaxial growth direction - is along the unit vector (0.69,0.72,0).