[Pw_forum] rhombohedral lattice wih R3c and R-3c: optimization

[Yue-Wen Fang]

Dear colleagues,

I want to calculate Volume-Energy data for R3c and R-3c BiFeO3,
respectively.

I started from a paraelectric R-3c BFO, after conducting ‘relax' with
constraining in different volumes (Bi and Fe atomic positions are fixed at
highly symmytrical points in each case), I find that at some volumes, the
symmetry of the structure is decreaed to R3c. In addition, for the similar
calculations starting from a ferroelectric R3c BFO, some structures become
R3 aftere realx calculations are done.

But, in order to get the V-E data, I think we must fix the space group
throughout the relax calculations. Is there any method which  can be used
to solve this problem?

Many thanks
Fang
-- 
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Yue-Wen FANG, PhD student
East China Normal University <http://english.ecnu.edu.cn/>, China
Japan Fine Ceramics Center, Japan
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