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[交流] 【求助】请教用abinit计算声子谱的一些问题

我在计算材料的声子谱的时候Gamma点的频率不分裂，但文献上说的是有分裂的，而且实验验证也是有分裂的，真诚请教各位高手：有谁遇到过这种问题，一般可能是什么原因造成的不分裂，先谢谢各位了..
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[ Last edited by wuli8 on 2009-3-30 at 16:42 ]

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1楼2009-03-30 16:09:12

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y1ding

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zdhlover(金币+2,VIP+0):谢谢 4-18 00:55
xiaoxue7002(金币+1,VIP+0):thank you 4-22 16:06

There is a good news about this result, and a bad news. The good news is that there are indeed three acoustic mode, with frequency rather close to zero (less than 1 cm^-1, which is rather good !). The bad news comes when the three other frequencies are compared with experimental results, or other theoretical results. Indeed, in the present run, one obtains three degenerate modes, while there should be a (2+1) splitting. This can be seen in the paper Ab initio calculation of phonon dispersions in semiconductors, by P. Giannozzi, S. de Gironcoli, P. Pavone and S. Baroni, Phys. Rev. B 43, 7231 (1991) , especially Fig. 2.

Actually, we have forgotten to take into account the coupling between atomic displacements and the homogeneous electric field, that exists in the case of polar insulators, for so-called "Longitudinal Optic (LO) modes". A splitting appears between these modes and the "Transverse Optic (TO) modes". This splitting (Lyddane-Sachs-Teller LO-TO splitting) is presented in simple terms in standard textbooks, and should not be forgotten in doing Ab initio calculations of phonon frequencies.

Thus we have now to treat correctly the homogeneous electric field type perturbation.