[DFTB-Plus-User] shell population in detailed.out

[agaur]

Dear all,

I have a question regarding "shell" and "orbital" population saved in 
the "detailed.out" file at the end of calculations. For example, ZnO 
calculations I used znorg S-K parameter set which specifies occupation 
for Zn as 10, 0, and 2 for d, p, and s orbitals of valence shell which I 
assume to be 3d, 4p, and 4s orbitals of Zn.

In detailed.out, the shell and orbital populations show the population 
for s, p, and d orbitals (reproduced below for ZnO wurtzite structure). 
Atoms 1 and are Zn, 3 and 4 are O. the population for Zn and O atoms 
does not show expected ionic behaviour (Zn+2 and O-2).

l-shell populations (up)
Atom Sh.   l     Population
1        1     0    0.60114443
1        2     1    0.89161710
1        3     2    9.96504343
2        1     0    0.60114443
2        2     1    0.89161710
2        3     2    9.96504343
3        1     0    1.84046368
3        2     1    4.70173136
4        1     0    1.84046368
4        2     1    4.70173136

1. Is the shell population in detailed.out is for the same orbitals 
(taken as valence shell/orbitals) in S-K parameters?
2. What is the reason for non-zero population in p orbital (shell-2)? Is 
4p orbital hybridized with 4s for Zn and the 2 electrons of 4s 
redistributed?
3. Does dftb+ describe ionic bonding (such as between Zn and O) 
accurately? Does this depend on the S-K parametrization?

Any help/clarification would be very useful. Thanks in advance.

Regards
Anshu Gaur
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