# [QE-users] Loewdin charges problem

Giuseppe Mattioli giuseppe.mattioli at ism.cnr.it
Thu Nov 1 16:49:25 CET 2018

```Dear Gui Wei

If you want to look for charge transfer, you should compare Lowdin
charges calculated for the two separated systems with those calculated
for the interacting system. Remember also that the projection of the
total density on the Lowdin basis set depends on the pseudopotentials
and that is never complete: at the very end of the projwfc.x output
there is a "spilling parameter", that represents the fraction of
charge that cannot be assigned to the Lowdin basis set. As this
quantity can be different in the case of nonintercating and
interacting systems, make careful assumptions on the grounds of the
results.
HTH
Giuseppe

Quoting Gui Wei <201707021019 at cqu.edu.cn>:

> Hi
> I am trying to calculate the charge transfer from graphene to
> iron.Firstly,I perform structural optimization calculation of
> Gr/Fe(110) system(1 Gr layer and 2 iron layer) and get optimized
> atomic coordinates.Secondly,I perform scf calculation and then use
> program projfwc.x to calculates the Loewdin charges.The ideal result
> I think is that Fe atom get the electrons and the C atom loose the
> electrons.Actually,C atom will donate its  electrons to the vacant
> d-orbitals of iron,result in donor–acceptor type interaction. But I
> can't get any meaningful information from the calculation
> results.For example,C(102) and Fe(11) form a bond (how to determine
> the type of bond ?) after structural optimization ,but the charge
> between them does not seem to shift compare to their valence
> electrons.
>
>
> C: Atom # 102: total charge =   3.9735, s =  0.8742, p =  3.0992, d
> =  0.0000,
> Fe: Atom # 11: total charge =   7.9832, s =  0.2977, p =  0.8703, d
> =  6.8152,
>  Spilling Parameter:   0.004
>
>
> What is the cause of the problem?
>
>
> Gui Wei

GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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E-mail: <giuseppe.mattioli at ism.cnr.it>

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