  We discuss the polarization responses in insulators in relation to the
quadrupole moment. The quadrupole moment is defined as the response of the free
energy to the gradient of the electric field, and its spatial variation results
in the polarization, similar to the relation between the Hall current and the
orbital magnetization. We show that a temperature gradient can induce
polarization, known as the thermopolarization effect and that the polarization
responses in insulators to the electric field and the temperature gradient
satisfy the Mott relation. These effects are observable as the Seebeck effect
in a finite-size system where the linear size is shorter than the screening
length.
