1972 年 33 巻 1 号 p. 12-20
A modified valence-force-field (VFF) model is applied to the lattice dynamics of trigonal selenium. Five adjustable parameters, four valence-force-constants (Kr, Kθ, Krr′, Krθ) within intra-chain couplings and one inter-chain force constant (KR), are determined from the observed six elastic constants by mans of the least squares method. By using these fore constants, comparable fits to the Γ-point optical frequencies for the A1, E1 and E2 modes are obtained except that for the A2 mode. However, the last can be also accounted for well if the contribution of about 50 cm−1 from the long-range electrostatic interaction is taken into account. The estimation of the above contribution seems reasonable from the view-point of the shell-model analysis due to Chen and Zallen [Phys. Rev. 173 (1968) 833]. In conclusion, the modified VFF employed here reflects the bonding in trigonal Se fairly well.
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