  We propose a new approach to study quantum phase transitions in
low-dimensional fermionic or spin models that go from uniform to spatially
inhomogeneous phases such as dimerized, trimerized, or incommensurate phases.
It is based on studying the length dependence of the von Neumann entropy and
its corresponding Fourier spectrum for finite segments in the ground state of
finite chains. Peaks at a nonzero wave vector are indicators of oscillatory
behavior in decaying correlation functions.
