I’m trying using PSI4 to constructe a complex state where the local spin of different parts in the system are antiferromagnetcally coupled.
According to the experience from using other softwares, the multiplicity for different parts could be set with opposite sign to represent the antiferromagnetic coupling. And, for the system I’m handling with, guess=mix wouldn’t be sufficient to get the wanted wavefunction due to the complexity of the coupling.
I accordingly tried fragment description for the molecule in PSI4, only to find there will be errors when set the fragment multiplicity to be minus values like -2.
Fatal Error: Illegal atom symbol in geometry specification: 0 on line
while the error will disappear if no minus multiplicity presents.
Is minus multiplicity supported currently, or is it possible to make a equivalent set in PSI4?
Besides, will SAPT0(UHF) support the broken-symmetry like dimer, such as one will encounter in the dissociation of H2, if Fragment had supported the minus multiplicity?
Thanks for your patience and looking forward to your reply.