I tried to parameterize a particular x-y-z-t dihedral angle of novel molecule using a Quantum Mechanical scan, but I got the strange result below.
The energy changes sharply around 130° and $E_\text{dihedral}(0°) \neq E_{dihedral}(360°)$. I performed PES scan in gaussian09 and psi4 and I got the same results in different softwares.
I'm uncertain what approach to take to fix the scan. I saw some parameterization articles which didn't perform PES scan 0-360 degree. Other authors performed scan in the range of 0-60 degree or 0-120 degree and I didn't predict I will face a result like this. What is going wrong with my scan and how can I fix the issue? Would performing single point energy for each angle instead of PES scan help?