There are four contributions to the **indirect spin-spin coupling constants**, namely

a) the **Fermi-Contact** contribution J_FC

b) the **Spin-Dipole** contribution J_SD

c) the **Paramagnetic Spin-Orbit** contribution J_PSO

d) the **Diamagnetic Spin-Orbit** contribution J_DSO.

Calculation of one of these contribution is requested via

**PROP=J_FC** (--> FC contribution)

**PROP=J_SD** (--> SD contribution)

**PROP=J_SO** (--> DSO and PSO contribution)

and is possible for all quantum chemical schemes, for which **analytic second derivatives** have been implemented for **UHF reference**
functions.

Note that, as the FC and the SD perturbations are **spin-dependent**, the calculation of these two contributions have to be currently
performed using a **UHF formalism**, i.e., necessitates specification of **REF=UHF** even for closed-shell molecules. on the other
side, calculation of the **spin-independent** SO contributions can be performed with a **closed-shell** reference.

As calculations of indirect spin-spin coupling are often hampered by **triplet instabilities**, the corresponding correlated
calculations are best performed using an **orbital unrelaxed** approach. The latter is invoked by specifying **DIFF_TYPE=UNRELAXED**.

If only a **subset** of indirect spin-spin coupling constants is needed, the calculations can be **restricted** such that only
for specific nuclei the corresponding FC, SD, or SO perturbations are considered (note that this means that all indirect
spin-spin coupling constants involving this nucleus or these nuclei are after calculations available indepedent of whether
the second nucleus is considered or not). The to be considered nuclei are specified via

%j_info

nucleus1

nucleus2

nucleus3

...

after the normal ZMAT input with atom1, atom2, atom3, ... giving the ZMAT number of the corresponding nuclei.

Note that in this way it is possible to
render otherwise too expensive calculations possible.

**Examples**

*Calculation of the FC contribution*

*Calculation of the SD contribution*

*Calculation of the SO contributions*

**Recommendations for the Calculation of Indirect Spin-Spin Coupling Constants**