Rémi
Since we (i.e. the nwchem developers) have never used ifort on the MACX64 platform,
an essential compiler option (-i8) is missing in your compilation.
My advise is to stick to gfortran, since that's the compiler we have been using.
The other option is to try to add the ifort option to the NWChem makefile structure.
Cheers, Edo