  Molecular ferroelectrics have attracted increasing interests over the past
decade due to mechanical flexibility, chemical diversity, environmental
friendliness, easy-processing, and lightness. The performance of molecular
ferroelectrics is approaching more and more competitive to their inorganic
counterparts. Despite the chemical diversity and tunability of the molecular
cations or anions, molecular ferroelectrics are not abundant. In particular,
physical directed design principles for new discovery or performance
optimization are still lacking. Here, through first-principles calculations, we
firstly reveal the importance of the molecular dipole moment of the polar
cations in a molecular perovskite ferroelectric, and then propose a molecular
dipole guided design rule for high-performance molecular ferroelectrics.
Finally, the rule is validated by first-principles calculations. We anticipate
that the rule is very useful in the field urging for new and high-performance
molecular ferroelectrics.
