What is the reference system that Q-Chem uses to compute the permanent dipole moment for a system with a non-0 charge? (the origin? centre of mass? …)
A separate issue, when opening an output in iQmol, the dipole that is printed on the GUI is not the one reported in the file. Does that dipole come from Mulliken charges?
I have no idea about IQmol, but within Q-Chem it should be the same coordinate system used for everything else. That is the standard nuclear orientation (principal axes of nuclear charge, printed just after the input file in the output), unless the user has disable that with NO_REORIENT = TRUE, in which case Q-Chem uses the molecular frame specified in the input file.
How different is the dipole from IQmol and from the output? Could it be simply the units – or the direction is different?
As John said, dipole is computed against the origin (000), which normally corresponds to the molecular COM, except when NO_REORIENT = TRUE is used.
Thank you all!
In the end, there is no issue with IQmol, my mistake