A new computational method for electronic-structure studies of molecules and solids is presented. The key element in the new model – denoted the perturbed atoms in molecules and solids model – is the concept of a perturbed atom in a complex. The basic approximation of the new model is unrestricted Hartree Fock (UHF). The UHF orbitals are localized by the Edmiston-Ruedenberg procedure. The perturbed ...