[Wien] How to obtain the input data of distorted lattice of non-cubic crystal?

[Peter Blaha]

I have not done such calculations myself. So you really must study the 
literature and there are many examples well described (I think there are 
at least papers by Mehl or D.Singh on these topics.)
>     (1) Which vector should be chosen to be mutiplied with the 
> strain matrix, primitive cell vectors or conventional cell vectors? For 
> the cubic structure,for example the TiC, the primitive cell vector is 
> different with the conventional cell vector. Please give me a clear 
> instruction about this point.

I guess you can do it either way. More convenient is working with 
convential cell.
>     (2) You said the strain matrix must be in the same system as the 
> bravais matrix. Here, is the bravais matrix is the conventional bravais 
> matrix? Or primitive bravais matrix? Which should be chosen? 
> Furthermore, taking the TiC as an example, the bravais matrix of TiC 
> should be cubic system, but the tetragonal train matrix and the 
> rhombohedral train matrix are chosen in the automatic calculation of 
> elastic constants by wien2k. Why?

I don't understand this question.
Of course, a certain strain matrix will lead to tetragonal or 
rhombohedral lattices. You cannot stay in cubic symmetry and get an 
information about an uniaxial strain.

>     (3) Comparing with the cartesian coordinates and fractional 
> coordinates of the original structure, will the respective coordinates 
> change of the distorted structure? If they do change, how will they 
> change, respectively?

Again I can't answer this question in a general way. At first they do 
not change, you just rigidly strain the cell.

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: 
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