Why is Iodine becoming Manganese when creating the .fchk file?


I’m pretty new to Psi4, and I am trying to generate a .fchk file for iodomethane with the following input.dat:

memory 1500 mb
set_num_threads (4)

molecule mol {

I -0.000001120230 -0.235257925013 0.000000000000
C 0.000007736812 1.921967634649 0.000000000000
H 0.516647802729 2.246305582223 -0.894827605797
H -1.033246667887 2.246327541223 0.000000000000
H 0.516647802729 2.246305582223 0.894827605797


set scf_type df
set basis def2-tzvpp
set reference uks


e, wfn = energy(‘B3LYP’, return_wfn=True)
oeprop(wfn, “MULLIKEN_CHARGES”)
fchk(wfn, ‘basistest.fchk’)

When I run this file, the atomic numbers of basistest.fchk read:

Atomic numbers I N= 5
25 6 1 1 1

I believe the first number should be 53 if the atom is Iodine, but for some reason the atomic number is 25 which is manganese. From what I understand, the def2-tzvpp basis set should work with Iodine. I would greatly appreciate any advice on how to fix this problem.

Which psi4 version?
This is ECP related and should be fixed in the latest version.

It is version 1.3.2. I’ll try updating to the latest version.

Thank you!