References
- Blume , M. , Emery , V. J. and Griffiths , R. B. 1971 . Phys. Rev. , A4 : 1071
- Mukamel , D. and Blume , M. 1974 . Phys. Rev. , A10 : 610
- Sivardiere , J. and Lajzerowicz , J. 1975 . Phys. Rev. , A11 : 2079
- 1975 . Phys. Rev. , A11 : 2090
- 1975 . Phys. Rev. , A11 : 2101
- Chakraborty , K. G. 1979 . Phys. Rev. , B20 : 2924
- Bernasconi , J. and Rys , F. 1971 . Phys. Rev. , B4 : 3045
- Buzano , C. 1988 . Physica , 150A : 54
- Blinc , R. and Zechs , B. 1974 . Soft Modes in Ferroelectrics and Antiferroelectrics , Amsterdam : North-Holland .