Nuclear spin-rotation constants

In DALTON the nuclear spin-rotation constants are calculated using rotational orbitals, giving an improved basis set convergence [74]. We use the expression for the spin-rotation constant where the paramagnetic term is evaluated around the center of mass, and thus will only solve three response equations at the most.

An input requesting the calculation of spin-rotation constants will look like

**DALTON INPUT
.RUN PROPERTIES
**WAVE FUNCTIONS
.HF
**PROPERTIES
.SPIN-R
.ISOTOP
    3
    2   1    1
**END OF DALTON INPUT

As the nuclear spin-rotation constants depend on the isotopic substitution of the molecule, both through the nuclear magnetic moments and through the center of mass, the isotopic constitution need to be specified if this is different from the most abundant isotopic constitution. Note that some of the most common isotopes do not have a magnetic moment.

For a SOPPA or SOPPA(CCSD) calculation of nuclear spin-rotation constants the additional keywords .SOPPA or .SOPPA(CCSD) have to be specified in the **PROPERTIES input module. For SOPPA an MP2 calculation has to be requested by the keyword .MP2 in the **WAVE FUNCTIONS input module, whereas for SOPPA(CCSD) a CCSD calculation has to be requested by the keyword .CC in the **WAVE FUNCTIONS input module with the *CC INPUT option .SOPPA(CCSD). This will also automatically disable the use of London orbitals.

We note that in the current release of DALTON, nuclear spin-rotation constants cannot be calculated employing symmetry-dependent nuclei. Thus for a molecule like N$_2$, the symmetry plane perpendicular to the molecular bond will have to be removed during the calculation.