Centrosymmetry
= Centrosymmetry
{wiki}
A crystal has centrosymmetry when its <crystallographic point group> contains spatial inversion. Its bulk electric-dipole polarization law must then satisfy $P(-E)=-P(E)$. Substituting a power expansion in E makes every even-order coefficient vanish, including the second-order <nonlinear optical susceptibility>. A surface, an external symmetry-breaking field or a response beyond the electric-dipole approximation can change the conclusion.