It is now possible to calculate certain open-shell magnetic field-related properties in Q-Chem. One is the hyperfine interaction (HFI) tensor, describing the interaction of unpaired electron spin with an atom’s nuclear spin levels:
where the Fermi contact (FC) contribution is
and the spin-dipole (SD) contribution is
for a nucleus .
Another sensitive probe of the individual nuclear environments in a molecule is the nuclear quadrupolar interaction (NQI), arising from the interaction of a nuclei’s quadrupole moment with an applied electric field gradient (EFG), calculated as
for a nucleus . Diagonalizing the tensor gives three principal values, ordered , which are components of the asymmetry parameter eta:
Both the hyperfine and EFG tensors are automatically calculated for all possible nuclei. All SCF-based methods (HF and DFT) are available with restricted and unrestricted references. Restricted open-shell references and post-HF methods are unavailable.
Only one keyword is necessary in the $rem section to activate the magnetic property module.
All other options are controlled through the $magnet input section, which has the same key-value format as the $rem section (see section 3.4). Current options are:
$rem method = hf basis = def2-sv(p) scf_convergence = 11 thresh = 14 symmetry = false sym_ignore = true magnet = true $end $magnet hyperfine = true electric = true $end $molecule 1 2 N 0.0000000000 0.0000000000 0.0000000000 C 1.4467530000 0.0000000000 0.0000000000 C 1.9682482963 0.0000000000 1.4334965024 O 1.2385450522 0.0000000000 2.4218667010 H 1.7988742211 -0.8959881458 -0.5223754133 H 1.7997303368 0.8930070757 -0.5235632630 H -0.4722340827 -0.0025218132 0.8996536532 H -0.5080000000 0.0766867527 -0.8765335943 O 3.3107284257 -0.0000000000 1.5849828121 H 3.9426948542 -0.0000000000 0.7289954096 $end