Fig. 4: Visualizing Hf–O bonds.
Computed electronic charge density for the unperturbed ferroelectric phase of HfO2 (panels a and b) as well as for the structures obtained at ηepi = −7 % (c and d) and ηepi = + 4 % (e and f). Panels a, c and e show a contour plot of the charge density within a plane that approximately contains the OI(1) atom highlighted in Fig. 1 as well as its three nearest-neighboring Hf atoms. Panels b, d and f show the charge density along lines connecting the central oxygen with each of its three nearest-neighboring Hf cations. In panel c, the red globe at the top left of the Hf(2) atom corresponds to a neighboring oxygen anion that gets close to the shown plane.
