The eigenstates of the finite system can be found in terms of the Bloch states of an infinite system with the same periodic potential. If there is a band gap between two consecutive energy bands of the infinite system, there is a sharp distinction between two types of states in the finite lattice. For each energy band of the infinite system, there are N − − 1 bulk states whose energies depend on the length N but not on the termination τ τ . These states are standing waves constructed as a superposition of two Bloch states with momenta k and − − k , where k is chosen so that the wavefunction vanishes at the boundaries. The energies of these states match the energy bands of the infinite system.