Jenny Du & John Stephenson
Optimization input files for benzene
#P RB3LYP 6-31G(D) OPT
Benzene
0,1
X1
X2 X1 1.0
C3 X2 RX2C X1 A1
C4 X2 RX2C X1 A1 C3 60.0
C5 X2 RX2C X1 A1 C4 60.0
C6 X2 RX2C X1 A1 C5 60.0
C7 X2 RX2C X1 A1 C6 60.0
C8 X2 RX2C X1 A1 C7 60.0
X9 C3 1.0 X2 A1 X1 0.0
H10 C3 RHC X9 A1 X2 180.0
H11 C4 RHC C3 A2 X2 180.0
H12 C5 RHC C4 A2 X2 180.0
H13 C6 RHC C5 A2 X2 180.0
H14 C7 RHC C6 A2 X2 180.0
H15 C8 RHC C7 A2 X2 180.0
A1 = 90.0
A2 = 120.0
RX2C = 1.3
RHC = 1.08
Optimization input files for fluorobenzene
#P RB3LYP 6-31G(D) OPT
Fluorobenzene
0,1
X1
X2 X1 1.0
C3 X2 RX2C X1 A1
C4 X2 RX2C X1 A1 C3 60.0
C5 X2 RX2C X1 A1 C4 60.0
C6 X2 RX2C X1 A1 C5 60.0
C7 X2 RX2C X1 A1 C6 60.0
C8 X2 RX2C X1 A1 C7 60.0
X9 C3 1.0 X2 A1 X1 0.0
F10 C3 RFC X9 A1 X2 180.0
H11 C4 RHC C3 A2 X2 180.0
H12 C5 RHC C4 A2 X2 180.0
H13 C6 RHC C5 A2 X2 180.0
H14 C7 RHC C6 A2 X2 180.0
H15 C8 RHC C7 A2 X2 180.0
A1 = 90.0

A2 = 120.0
RX2C = 1.3
RHC = 1.08
RFC = 1.10
Electron density input files for benzene a%chk=B2
#P RB3LYP 6-31G(D) Cube(40,Potential)
Benzene
0,1
C .000000 1.396606 .000000
C 1.209497 .698303 .000000
C 1.209497 -.698303 .000000
C .000000 -1.396606 .000000
C -1.209497 -.698303 .000000
C -1.209497 .698303 .000000
H .000000 2.483628 .000000
H 2.150885 1.241814 .000000
H 2.150885 -1.241814 .000000
H .000000 -2.483628 .000000
H -2.150885 -1.241814 .000000
H -2.150885 1.241814 .000000 benzene.data
Electron density input files for fluorobenzene a%chk=FB2
#P RB3LYP 6-31G(D) Cube(40,Potential)
Fluorobenzene
0,1
C .000000 .000000 .931377
C .000000 1.217575 .260461
C .000000 1.208689 -1.135489
C .000000 .000000 -1.835719
C .000000 -1.208689 -1.135489
C .000000 -1.217575 .260461
F .000000 .000000 2.282350
H .000000 2.141867 .828928
H .000000 2.151569 -1.675421
H .000000 .000000 -2.921785
H .000000 -2.151569 -1.675421
H .000000 -2.141867 .828928 fluorobenzene.data

Pictures of electron density for fluorobenzene and benzene respectively:
In the electron density plot of fluorobenzene, it can be observed that there is greater electron density around the fluorine atom in comparison to the hydrogen atoms. This can be attributed to the higher electronegativity of the fluorine atom, and hence a greater tendency to pull electrons (i.e. negative charge) towards itself. There is also a considerable distribution of the electron density around the carbon atoms, and this may be explained by the presence of pi-bonding within the aromatic structure.
The electron density plot of benzene essentially depicts the same information. However, the electron distribution is symmetric over the whole molecule, because there are no substituents on the ring that have a different electronegativity.