Electron Spectrum of Gapless Semiconductors

1. Introduction.- 2. Band-Structure Calculation Methods.- 2.1 Adiabatic Approximation.- 2.2 The One-Electron Hartree-Fock Approximation.- 2.3 Correlation Phenomena.- 2.4 Methods Used to Solve the Schrödinger Equation.- 3. Insulators, Semiconductors, Metals.- 3.1 The Detection of the Gapless State.- 3.2 Gray Tin.- 3.3 Mercury Chalcogenides HgTe and HgSe.- 4. Impurities.- 4.1 The Problem of Residual Electron Concentration.- 4.2 Impurities and Intrinsic Defects in Mercury Chalcogenides..- 4.3 Energies of Impurity States.- 4.4 Metal-Insulator Transitions.- 4.5 The Mott Transition in n-Type Crystals.- 4.6 The Influence of Compensation on the Mott Transition.- 4.7 An "Anomaly" in the Temperature Dependence of the Electron Concentration.- 4.8 Freeze-Out of Electrons onto Acceptors in a Magnetic Field.- 4.9 Freeze-Out of Electrons onto Acceptors Subject to Hydrostatic Pressure.- 4.10 On the Mobility of Holes in Gapless HgCdTe Crystals.- 5. Semimagnetic Semiconductors.- 5.1 HgMnTe Crystals.- 5.2 HgSe:Fe Crystals.- 5.4 DX Centers.- 5.5 The Improved Short-Range Correlation Model.- 6. Conclusion.- 6.1 Practical Applications of Gapless Semiconductors.- 6.2 Some Results and Problems.- References.