There are couple of option

1. Bader analysis
2. Charge density difference (plot in vesta is easy). Take CHGCAR(A+B) and subtract CHGCAR(A) and CHGCAR(B). It can be easily done in vesta >edit> volumetric data
3. Mulken population analysis (use chgmol programme)

There are couple of options:

1. Bader analysis
2. Charge density difference (plot in vesta is easy). Take CHGCAR(A+B) and subtract CHGCAR(A) and CHGCAR(B). It can be easily done in vesta >edit> volumetric data
3. Mulken population analysis (use chgmol programme)