[Wien] Formation energy + some other querries!

[Nandan Tandon]

Dear Prof Blaha

I am still not convinced that the zero of energy is not required.

When we are considering the differences in the single particle energies
for a particular system, I agree that the arbitrary number representing
the zero is not required since it cancels but for differences in total
energies of different systems will require the zero reference.

I will explain my problem in detail :

I wish to find the formation energy for a Mn impurity in GaN. I do a
supercell calculation (32 atom per unit cell) for pure GaN and Mn
substituted GaN. I also calculate the energy of a single Mn atom and a
single Ga atom by putting in a large unit cell. Then the formation energy
is

FE = E(Ga_16N_16) + E(Mn) - E(Ga)- E(Ga_15MnN_16)

Each of the above total energies are with respect to the respective zero
energy for that system. Is it that when wien gives the total energy per
unit cell for any system, it takes care of the reference level?

Regards

Anjali Kshirsagar

On 2/5/08, Peter Blaha <pblaha at theochem.tuwien.ac.at> wrote:
> > 1. We need to calculate the Formation energies for impurities in some
> > semiconductor material. Thus an algebra with the total energies of different
> > systems. I therefore need to know the zero of my energy. I am not able to find
> > where this value is written. Should be in case.scf0. Can you please tell us
> > where to look for average interstitial potential or the zero of energy for a
> > particular case?
>
> I don't think you need to know the zero of your energy. It is an arbitrary number.
>
> > 2. This problem we are facing with the 06, 07 versions. Earlier, there was a
> > provision in case.in1 file that unit could be specified and accordingly the
> > k-list will be read from in1 or case.klist file. Now the program does not allow
> > us to read the k-list from in1. Why such a change has been made? Actually I
> > find that there is a rewind command for the specific unit and if it is unit 5,
> > case.in1 is rewind and there is an error. I did not see any such problem on the
> > mailing list. We also posted the question but there was no reply even after
> > putting it 2-3 times. Hence I want to knwo if we are making any error or is
> > there a problem. I will accordingly send you the actual files and the error we
> > are getting.
>
> Using unit=5 for the k-vector list is not recommended. It should still be possible,
> but you need an extra line before the k-list (put 1.d-15) and the k-list must be in the new
> format (4I10 instead of 4I5, check the new klist format).
> Unfortunately the UG has not been updated properly.
>
> > 3. We are also not able to run self-consistency for Monkhost mesh/ special
> > k-points? Please guide us where to get the information regarding this. We are
> > doing slab calculations and for the large supercell we wish to use Monkhost
> > mesh for reducing the computations.
>
> You can put ANY k-mesh into case.klist; specify TEMP (or GAUSS) for the Fermi-method
> and run an scf-cycle. (KGEN produces a special point mesh anyway, only for centered
> lattices it is different due to symmetry constrains).
>
> --
>
>                                        P.Blaha
> --------------------------------------------------------------------------
> 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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