5.25. MP2 Level Magnetic Properties

Presently, hyperfine couplings (excluding the \(A_\text{orb}\) term), g-tensors, and shielding tensors without GIAOs can be calculated for both canonical and RI-MP2 and double-hybrid DFT without the frozen core approximation. The \(A_\text{orb}\) term of the hyperfine couplings is available only for RI-MP2 and double-hybrid DFT with and without frozen core approximation. In case the RIJCOSX approximation is used, the keywords Z_GridX, Z_GridX_RHS, KCOpt, KC_GridX and KC_IntAccX are relevant – see sections RIJCOSX-RI-MP2 Gradients and MP2 and RI-MP2 Second Derivatives. NMR shielding and g-tensor calculations with GIAOs are available for RI-MP2 and double-hybrid DFT with or without a frozen core. The implementation is described in detail in refs [345, 346] and the available options are shown in section RI-MP2 and Double-Hybrid DFT Response Properties. Note that for double-hybrid DFT the correct properties are printed after the density heading containing “Method : MP2” and “Level : Relaxed density”. DLPNO-MP2 (and double-hybrid) shielding tensors are also available - see section Local MP2 Second Derivatives and Response Properties.

5.25.1. Calculating Properties from Existing Densities

Occasionally, one may calculate a density matrix using an expensive correlated method such as CCSD and realize afterwards that a certain property such as the quadrupole moment or a hyperfine coupling constant (HFCC) is also required. Rather than start the whole calculation from scratch, one may wish to use the existing density matrix to calculate the properties. For this purpose, we have experimentally introduced a “properties only” calculation mode, whereby the MOs are read from an existing BaseName.gbw file and the densities are read from an existing BaseName.densities file and only the property calculations are performed. Note however, that this presents many possibilities for error, so only use it as a last resort and be very careful with the results!

Take, for example, this CCSD calculation:

! CCSD def2-SVP

%base "BO-CCSD"

%mdci density unrelaxed end

*xyz 0 2
B 0 0 0
O 0 0 1.2049
*

This produces the files BO-CCSD.gbw and BO-CCSD.densities. To obtain the CCSD quadrupole moment and HFCCs without repeating the whole calculation, we can copy these two files into a new directory (highly recommended!) and start a second job with the !PropertiesOnly keyword. Note that the basename of the second job must be identical!

! CCSD def2-SVP

%base "BO-CCSD"

%mdci density unrelaxed end

*xyz 0 2
B 0 0 0
O 0 0 1.2049
*
# Everything above must be the same as in the first job!

# Request the property calculations
! PropertiesOnly 
%elprop
  quadrupole true
end
%eprnmr
  Nuclei = all B { Aiso, Adip }
  Nuclei = all O { Aiso, Adip }
end