Fig. 2: Intrinsic OOP AFE in bilayer GeSe by first-principles calculations.
From: Unconventional (anti)ferroelectricity in van der Waals group-IV monochalcogenides
a Freestanding monolayer (ML). b freestanding AB-stacking bilayer. c Fixed A layer in bilayer GeSe in (b). d Fixed B layer in bilayer in (b). The ϕi (i = 1, 2, A-1, A-2, B-1, B-2, AB-1, AB-2) in a–d indicates the vacuum energy level. e–h Electrostatic potential energy of the freestanding monolayer (e), AB-stacking bilayer (f), the fixed A layer (g), and the fixed B layer (h), where z0 is the thickness of the unit cell, z is a coordinate variable, and z/z0 refers to the relative position in the unit cell. i Total energy of bilayer GeSe with external electric fields. j Total energy of bilayer GeSe with removal of the external electric fields yet preserving the electric field-tuned structures of the bilayer. The curves around the critical electric fields are highlighted by red squares and magnified panels. k Electric field dependence of the potential energy difference and the polarization for the A and B layers.
