  Originating from a broken spatial inversion symmetry, ferroelectricity is a
functionality of materials with an electric dipole that can be switched by
external electric fields. Spontaneous polarization is a crucial ferroelectric
property, and its amplitude is determined by the strength of polar structural
distortions. Density functional theory (DFT) is one of the most widely used
theoretical methods to study ferroelectric properties, yet it is limited by the
levels of approximations in electron exchange-correlation. On the one hand, the
local density approximation (LDA) is considered to be more accurate for the
conventional perovskite ferroelectrics such as BaTiO3 and PbTiO3 than the
generalized gradient approximation (GGA), which suffers from the so-called
super-tetragonality error. On the other hand, GGA is more suitable for
hydrogen-bonded ferroelectrics than LDA, which largely overestimates the
strength of hydrogen bonding in general. We show here that the recently
developed general-purpose strongly constrained and appropriately normed (SCAN)
meta-GGA functional significantly improves over the traditional LDA/GGA for
structural, electric, and energetic properties of diversely-bonded
ferroelectric materials with a comparable computational effort, and thus
enhances largely the predictive power of DFT in studies of ferroelectric
materials. We also address the observed system-dependent performances of LDA
and GGA for ferroelectrics from a chemical bonding point of view.
