Why is charge transfer a problem in DFT

[Sigmund]

Charge transfer is often referred to as a problem in conjunction with DFT, Density Functional Theory.

Why is it so?

Consider an electron attached to a molecule with positive electron affinity.

We first calculate the electron density. Then we change the positions of the nuclei a little. Then we calculate the electron density again. The electron density has probably changed somewhat. Is this redistribution of electron density referred to as "charge transfer"? And is it in any way a problem for DFT? Should TDDFT be used?

[Sovereign]

Charge transfer is often referred to as a problem in conjunction with DFT, Density Functional Theory.

Why is it so?

Consider an electron attached to a molecule with positive electron affinity.

We first calculate the electron density. Then we change the positions of the nuclei a little. Then we calculate the electron density again. The electron density has probably changed somewhat. Is this redistribution of electron density referred to as "charge transfer"? And is it in any way a problem for DFT? Should TDDFT be used?

 

Charge transfer implies moving charge from one location to another. In order for something to move it has to exist. So what is this thing called charge that moves? Is it a little ball attached to a particle that sticks to another particle?