[Wien] Question regarding volume optimization

[Stefaan Cottenier]

> I have a query regarding volume optimization in wien2k. "Option 1"
> optimizes the volume by keeping a:b:c = constant. Now my question is:
>
> in which case this "Option 1" is applicable?...is it only applicable for
> cubic symmetry?

You can use it for any crystal. Very often, the total energy will 
depends much more on the volume than on the c/a- or b/a-ratio.

The difference between cubic and other crystals is that for a cubic 
crystal it is meaningless to vary anything else than the volume.

Similarly, for a tetragonal crystal you can change the volume and c/a, 
but not b/a. For an orthorombic crystal can change volume, c/a, b/a. Etc.

Stefaan