Questions about MullikenPopulation

[vboyz]

hi！i studied the MullikenPopulation calculation and i am puzzled that why the total of MullikenPopulation result of a molecule is not zero?
as i know, the melecular without bias is neutral electricity. But as the manual gives:
O: 5.88901735645
H: 1.05566628484
H: 1.05531635871
The total charge of H2O melecule is not zero. Can you explain it for me ? Thanks!

BTW,I use Dmol3 before i learn ATK，when dmol give the population of atomic charge, the total are always zero, so i cannot understand the result of ATK well. I think they may different.

[Anders Blom]

The Mulliken populations are not the net charges on the atoms, but the number of electrons (which may be a non-integer number) associated with each atom. If you sum the 3 numbers you get 8 = the number of valence electrons in the basis set.

To calculate the net charge on each atom, subtract the atomic valence charge (6 for oxygen and 1 for hydrogen), and you get
O: -0.11098264355
H: 0.05566628484
H: 0.05531635871
These add up to zero.

[vboyz]

So how do deal with transition metal ? use its valence electrons as same ?

[vboyz]

OK,I find the atomic data in the manual. thanks all the same!
But if i use SZP or DZP,does it perform different valence electrons?

[Anders Blom]

No, the valence is the same for all basis sets. The valence electrons just have more orbitals to "spread out" onto, to give variational freedom to describe different types of radial and angular bonding characteristics.