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3. A. Zunger, J. Phys. Chem. Solids36, 229 (1975); G. Pastori- Parraviccini, F. Piccini and L. Resca, Phys. Stat. Sol.60, 801 (1972); E. L. Pollack, T. A. Bruce, G. V. Chester and J. Krumhansl, Phys. Rev. B5, 4180 (1972); J. A. Krumhansl and S. Y. Wu, Phys. Rev. B5, 4155 (1972); D. M. Gray and A.Gray, Phys. Rev. B19, 5329 (1979); L. Kumar, H. J. Monkhorst and J. Oddershede, Int. J. Quant. Chem.12, 145; (1978); C. Friedli and N. W. Ashcroft, Phys. Rev. B16, 662 (1977).
4. A. Zunger, J. Phys. Chem. Solids36, 229 (1975); G. Pastori- Parraviccini, F. Piccini and L. Resca, Phys. Stat. Sol.60, 801 (1972); E. L. Pollack, T. A. Bruce, G. V. Chester and J. Krumhansl, Phys. Rev. B5, 4180 (1972); J. A. Krumhansl and S. Y. Wu, Phys. Rev. B5, 4155 (1972); D. M. Gray and A.Gray, Phys. Rev. B19, 5329 (1979); L. Kumar, H. J. Monkhorst and J. Oddershede, Int. J. Quant. Chem.12, 145; (1978); C. Friedli and N. W. Ashcroft, Phys. Rev. B16, 662 (1977).
5. A. Zunger, J. Phys. Chem. Solids36, 229 (1975); G. Pastori- Parraviccini, F. Piccini and L. Resca, Phys. Stat. Sol.60, 801 (1972); E. L. Pollack, T. A. Bruce, G. V. Chester and J. Krumhansl, Phys. Rev. B5, 4180 (1972); J. A. Krumhansl and S. Y. Wu, Phys. Rev. B5, 4155 (1972); D. M. Gray and A.Gray, Phys. Rev. B19, 5329 (1979); L. Kumar, H. J. Monkhorst and J. Oddershede, Int. J. Quant. Chem.12, 145; (1978); C. Friedli and N. W. Ashcroft, Phys. Rev. B16, 662 (1977).