Thank you for your detailed answer in Convergene Algorithms. I will answer here as my answer is related to this topic.
After switching to the cc-pvdz basis set, reference uks or rohf and using the read guess, I still encounter convergence issues. Actually, with the others set-up (sad guess, default reference and cc-pvqz or def2-tzvppd basis sets), the calculations with Chloride and Bromide converged. I also have a problem with the fact that the cc-pvdz basis is not defined for iodide which I am interested in. The basis sets available for Iodide contains ECP (def2-tzvppd) or PP (pseudopotential, cc-pvdz-pp) basis sets. Mind you, the cc-pvdz-pp is not already defined for iodide so I used the Psi4 basis set library route from user-defined basis set section to add it as cc-pvdz-pp-ri.gbs in the Psi4 basis set library(I am net to GitHub so I did not know if it is worth a PR or not). Once it will be verified and added, I will try to run Iodide using this basis set. However, I doubt it will work.
Just so you have the big picture of what I am doing, here is a rough summary. I am calculating interaction energy scan from 1.5 to 6.0 Angstroms of Iodide, Chloride or Bromide with compounds such as benzene, imidazole, indole, methanol, methanethiol, methylguanidium and N-methylacetamide among others. For Chloride and Bromide, I was able to try several basis sets (cc-pvqz, def2-tzvppd) as they are available for them. The real struggle is with iodide.
I can upload all the inputs that worked with iodide to let you see and maybe you will be able to help me with my issue.
Thank you again for your time and help.