  Recent studies highlight the scientific importance and broad application
prospects of two-dimensional (2D) sliding ferroelectrics, which prevalently
exhibit vertical polarization with suitable stackings. It is crucial to
understand the mechanisms of sliding ferroelectricity and to deterministically
and efficiently switch the polarization with optimized electric fields. Here,
applying our newly developed DREAM-Allegro multi-task equivariant neural
network, which simultaneously predicts interatomic potentials and Born
effective charges, we construct a comprehensive potential for boron nitride
($\mathrm{BN}$) bilayer. The molecular dynamics simulations reveal a remarkably
high Curie temperature of up to 1500K, facilitated by robust intralayer
chemical bonds and delicate interlayer van der Waals(vdW) interactions. More
importantly, it is found that, compared to the out-of-plane electric field, the
inclined field not only leads to deterministic switching of electric
polarization, but also largely lower the critical strength of field, due to the
presence of the in-plane polarization in the transition state. This strategy of
an inclined field is demonstrated to be universal for other sliding
ferroelectric systems with monolayer structures belonging to the symmetry group
$p \bar{6} m 2$, such as transition metal dichalcogenides (TMDs).
