Good Morning,

I am new in using Psi4 and I have some problems with the potential energies for the dihedral angle of the Ethylene Glycol.

I ran different codes (changing some parameters) but the Potential Energies are always the same for all the angles (more or less). My purpose is to plot these energies to find the different conformers of this molecule.

Here is one of the codes that I used.

It will be a pleasure for me if someone can help me and explain me why the energies are all the same.

```
molecule Ethylene_Glycol{
0 1
H
C 1 r2
H 2 r3 1 a3
O 2 r4 1 a4 3 d4
H 4 r5 2 a5 1 d5
C 2 r6 1 a6 3 d6
H 6 r7 2 a7 1 d7
H 6 r8 2 a8 1 d8
O 6 r9 2 a9 1 d9
H 9 r10 6 a10 2 d10
r2= 1.1107
r3= 1.1139
a3= 107.32
r4= 1.4014
a4= 108.51
d4= 119.25
r5= 0.9929
a5= 106.65
d5= 198.10
r6= 1.5276
a6= 109.46
d6= 239.75
r7= 1.1107
a7= 109.46
d7= 299.05
r8= 1.1139
a8= 110.75
d8= 180.92
r9= 1.4014
a9= 110.37
d9= 58.41
r10= 0.9929
a10= 106.65
d10= 78.17
}
#optimize molecule at different dihedral angles
steps = 37
step_size = 10
start_angle = 0
ecp = {}
for counter in range (0, steps):
# set smaller basis set for geometry HT geometry optimization
set {
basis sto-3g
geom_maxiter 100
scf_type df
guess sad
ints_tolerance 1.0E-8
}
dihedral = 1.0 * counter * step_size + start_angle
dihedral_string = "2 4 6 9%.1f" % dihedral
set optking {
frozen_dihedral = ""
fixed_dihedral = $dihedral_string
}
optimize('scf') # geometry optimization with HF
#change basis set for single point energy calculation
set {
basis cc-pVDZ
scf_type df
guess sad
}
ecp[counter] = energy('scf')
psi4.print_out("\n")
psi4.print_out("Energies for different dihedral angles with sto-3g \n\n")
psi4.print_out(" Dihedral [degree] E_int [kcal/mol] \n")
psi4.print_out("-----------------------------------------------------\n")
for counter in range (0, steps):
dihedral = 1.0 * counter * step_size + start_angle
e = ecp[counter] * psi_hartree2kcalmol
psi4.print_out(" %3.1f %10.6f\n" % (dihedral, e))
```

Thank you so much!