[Wien] SuperCell Calculation, space group and total energy

[Peter Blaha]

Most likely some parameters (eg. k-mesh) were not consistent.

I suggest to run the distorted structure, save the results, move the atom back
to its original position and rerun an scf cycle (without initialization.

This way you are using identical parameters.

Cara Watson schrieb:
> Dear Wien2k users,
> 
> I want to do the calculation on modified TiC structure (displacing an
> atom with respect to other atoms). So I used a 1*1*1 supercell with 8
> inequivalent atoms (4 Ti 4 C). First time I run initialization with
> all atoms sitting on their equilibrium positions, and "sgroup" told me
> the space group is 225Fm3m, I accepted it and ran the calculation, I
> got a total energy. Later on, I started another TiC structure by
> shifting a Ti atom a little bit towards its neighboring C atom (but
> fix all other 7 atoms) and ran the initialization, the sgroup told me
> the space group is 99, I accepted it again and ran the calculation,
> then got another total energy.
> 
> However, the confusion I got is that the total energy of the
> equilibrium one is even higher than the energy of the shifted one
> which is unphysical!
> 
> So I was wondering if these two total energies came from different
> space groups are not actually comparable (e.g., difference energy
> reference points)? Or do you have some explanations on this in your
> mind?
> 
> Thanks!
> Cara
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                                       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: http://info.tuwien.ac.at/theochem/
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