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

[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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