The nearly-free electron debacle showed researchers that any model that assumed that ions were in a sea of free electrons needed modification. So, a number of quantum mechanical models—such as band structure calculations based on molecular orbitals or the density functional theory—were developed. In these models, one either departs from the atomic orbitals of neutral atoms that share their electrons or (in the case of density functional theory) departs from the total electron density. The free-electron picture has, nevertheless, remained a dominant one in education.