[Wien] [Wien2k User Group] Lattice stability in bcc, fcc and hcp and other crystal structures

[Stefaan Cottenier]

> The stable phases of uranium are C-centered orthorhombic (alpha), primitive
> tetragonal(beta) and fcc (gamma).
> Getting the atomic positions of these phases from ICSD, I can calculate the
> ENE (ground state energy). I need not do any min_lapw since these are stable
> phases.

That last statement is a peculiar one. It implies you assume that any  
structure taken from ICSD will give you zero forces...? And no further  
energy lowering if you (slightly) change cell size and shape...? A  
perfect agreement between theory and experiment? Hmmm...

> Now I imagine uranium in hcp phase of any metal like any refractory element
> (which are usually in hcp) (Blaha's papers on hcp metals are a good starting
> point). I replace the hcp crystal structure with uranium only. Then I
> calculate the ENE.
> This is the ENE of uranium in the metastable phase. I guess I am right.

And which 'a' and 'c' lattice parameters are you going to take for  
hcp-U? You can make a smart guess, but in the end you'll find yourself  
making a 2D scan of energies as a function of 'a' and 'c' to find the  
optimal prediction for the cell size and shape.

Stefaan