[Wien] valence s-charge density of 7Be in Cu and Al

[Peter Blaha]

How big is your supercell ? How many atoms ??

I expect it is much too small ! Use a supercell as large as possible
on your computer, but definitely it should be at least 64 - 256 atoms.

If Be has a very different volume compared to the host, it needs space
and this requires that the Cu atoms can move away slightly over a long range.

Am 07.12.2010 13:58, schrieb Amlan Ray:
> Dear Prof. Blaha,
> Thank you for your reply regarding the valence s-electron density plot. Actually I am studying the cases of implantation of 7Be in aluminum and copper lattices. We have formed
> supercells (using both neighbors and 2nd neighbors and the force minimization) with the 7Be at octahedral positions and done the calculations. We found that the total electron
> density at 7Be nucleus increases by about 0.5% when 7Be is implanted in the smaller copper lattice. The result is about the same whether both 1s and 2s orbitals of 7Be are treated
> as valence electrons or 1s as core and 2s as valence. (The experimental result is in the opposite direction. It shows the decay rate is faster in aluminum by (0.18+-0.13)%).
> I think the predicted increase of the electron density when 7Be is implanted in copper is because of the substantially smaller spatial dimension of the copper lattice. If I run
> the code the using 1s orbital of 7Be as core and 2s as valence, then I find that the 2s electron density at 7Be nucleus increases by about 26% when 7Be is in copper. In order to
> probe further, I plotted the total valence electron charge density of 7Be as a function of the distance from 7Be nucleus (please see the attached .pdf plot). Although in the
> attached plot, I am showing the total valence charge density, the bump around 0.25 BU appears to be the first bump of 2s electron orbital. The second larger bump of 2s orbital
> apparently got mixed up with other valence orbitals and I did not show it in the attached plot. The dash-dot line is for 7Be in Cu and the solid line is for 7Be in Al. So it looks
> like that we are getting 26% higher 2s electron density when 7Be is in copper, because there is more (about 26%) 2s electrons in 7Be when implanted in copper. However the smaller
> spatial dimension of copper has not pushed the 2s orbital closer to the nucleus. The 2s orbital seems to be at the right place. I have also looked at the density of states versus
> energy plot for the valence s-electrons of 7Be. I find that for 7Be in Al, the energy of the s-electrons lie from about (--3 eV to +8.4 eV(Fermi energy)) and for 7Be in Cu, the
> energy of the s-electrons lies from (-1.3 eV to +10.8 eV (Fermi energy)). The total number of valence s-electrons of 7Be is more when 7Be is in Al.
> I am somewhat puzzled to find that as the energy of valence s-electrons of 7Be in Cu is increasing considerably (compared to implantation in Al) and the total number of valence
> s-electrons summed up to Fermi energy is decreasing, the number of electrons in the characteristic first bump of 2s orbital is increasing, thus increasing the 2s electron density
> at the nucleus. I was expecting that the copper having higher electron affinity would take away s-electrons from 7Be reducing the number of 2s electrons and the corresponding
> charge density at the nucleus as found experimentally.
> With best regards
> Amlan Ray
> Address
> Amlan Ray
> Variable Energy Cyclotron Center
> 1/AF, Bidhan Nagar
> Kolkata - 700064
> India
>
>
>
>
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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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