  Traditional ferroelectrics are limited by Neumann's principle, which confines
exploration of ferroelectrics within polar point groups. Our recent work [Nat.
Commun. 15, 135, (2024)] proposes the concept of fractional quantum
ferroelectricity (FQFE) that extend the playground of ferroelectricity to
non-polar point groups. Here, we apply group theory and introduce an efficient
symmetry strategy to identify FQFE candidates. Integrated with a
high-throughput screening scheme, we go through 171,527 materials and identify
202 potential FQFE candidates, which are already experimentally synthesized. In
addition, we point out that the essence of FQFE is fractional atomic
displacements with respect to lattice vectors, which can actually result in
both fractional (type-I) and integer (type-II) quantized polarization,
respectively. Through performing first-principles calculations, we verify the
symmetry-predicted switchable FQFE properties in bulk AlAgS2 and monolayer
HgI2. Notably, AlAgS2 exhibits an ultra-low switching barrier of 23 meV/f.u.
and interlocked in-plane/out-of-plane polarization, while HgI2 demonstrates
large spontaneous polarization of 42 {\mu}C/cm2. Our findings not only advance
the understanding on FQFE, but also offer guidance for experimental exploration
and design of novel ferroelectric materials.
