Quantum chemistry of macromolecules and solids.

Two classes of electronic structure methods for macromolecules and nonmetallic solids are reviewed, showcasing their applications to hydrocarbon polymers and organic molecular crystals. One is the crystalline orbital theory for periodic extended systems and the other is a localized-orbital, embedding-field approach for periodic or nonperiodic systems consisting of weakly-interacting subsystems. Both implement rigorous electron-correlation theories such as coupled-cluster and perturbation theories as well as density-functional approximations and can treat not just ground-state energies but also equilibrium structures, phonons (in the harmonic approximation and beyond), excitons, and quasiparticle energy bands (by the crystalline orbital theory only). Three key concepts underlying macromolecular and solid-state electronic structure theories--decay of effective inter-particle interactions, size extensivity, and periodicity--are identified and analyzed in the context of these two closely related approaches.