This chapter starts out a short, two-chapter section on very basic mathematics of quantum mechanics, appropriate for those who have taken undergraduate science or engineering courses. The method of “unit analysis” is used as a way of getting at when quantum mechanics will play a role in the behavior of things.

The chapter starts with the derivation of effective Hamiltonian for band electrons in magnetic field and continues with discussion of energy levels in magnetic field for massless Dirac fermions. The case of bilayer graphene is also considered. Special attention is paid to a formation of topologically protected zero-energy modes. Using band electrons in magnetic field as an example, a general concept of Berry phase is introduced. Magneto-oscillation effects for two-dimensional Dirac fermions are considered. Quantum Hall effect is discussed, via topological approach by Thouless and coworkers. At the end, we discuss electronic structure in the presence of crossed electric and magnetic fields and the effects of a smooth disorder on Landau levels for massless Dirac electrons.

Boundary conditions for electron wave functions in graphene are discussed, both in Dirac approximation and for the honeycomb lattice. We start with the model of "neutrino billiard." Then, we discuss typicality of zigzag boundary conditions for the terminated honeycomb lattice, existence of zero-energy edge mode for these conditions, electronic states and conductance quantization in graphene nanoribbons, level statistics for graphene quantum dots, explanation of quantum Hall effects in terms of topologically protected edge modes, and Aharonov–Bohm effect in multiconnected graphene flakes. The latter case is used as an example of the general topological concept of spectral flow.