A series of calculations on MgB2 and related isoelectronic systems indicates that the layer of Mg 2+ ions lowers the non-bonding B π (pz) bands relative to the bonding σ (spxpy) bands compared to graphite, causing σ → π charge transfer and σ band doping of 0.13 holes/cell. Due to their two dimensionality the σ bands contribute strongly to the Fermi level density of states. Calculated deformation potentials of Γ point phonons identify the B bond stretching modes as dominating the electron-phonon coupling. Superconductivity driven by σ band holes is consistent with the report of destruction of superconductivity by doping with Al.

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A pronounced uniform polar distortion extending over several unit cells enables thin LaAlO3 overlayers on SrTiO3(001) to counteract the charge dipole and thereby neutralize the "polarization catastrophe" that is suggested by simple ion counting. This unanticipated mechanism, obtained from density functional theory calculations, allows several unit cells of the LaAlO3 overlayer to remain insulating (hence, fully ionic). The band gap of the system, defined by occupied O 2p states at the surface and unoccupied Ti 3d states at the interface in some cases approximately 20 A distant, decreases with increasing thickness of the LaAlO3 film before an insulator-to-metal transition and a crossover to an electronic reconstruction occurs at around five monolayers of LaAlO3.

When either electron or hole doped at concentrations x ∼ 0.1, the LaOFeAs family displays remarkably high temperature superconductivity with Tc up to 55 K. In the most energetically stable QM = (π, π) antiferromagnetic (AFM) phase comprised of tetragonal-symmetry breaking alternating chains of aligned spins, there is a deep pseudogap in the Fe 3d states centered at the Fermi energy, and very strong magnetophonon coupling is uncovered. Doping (of either sign) beyond x ∼ 0.1 results in Fe 3d heavy mass carriers (m * ∼ 4 − 8) with a large Fermi surface. Calculated Fe-Fe transverse exchange couplings Jij (R) reveal that exchange coupling is strongly dependent on the AFM symmetry and Fe-As distance.