This chapter describes the calculation of properties depending on magnetic fields, both as created by an external magnetic field as well as the magnetic field created by a nuclear magnetic moment. This includes the two contributions to the ordinary spin-Hamiltonian used in NMR, nuclear shieldings and indirect nuclear spin-spin couplings constants. We also describe the calculation of the magnetic analogue of the polarizability, the molecular magnetizability. This property is of importance in NMR experiments where the reference substance is placed in another tube than the sample. We also shortly describe two properties very closely related to the magnetizability and nuclear shieldings, respectively, the rotational g factor and the nuclear spin-rotation constants.
Three properties that in principle depend on the magnetic moments are
not treated here, namely the properties associated with optical
activity or, more precisely, with circular dichroism. These
properties are Vibrational Circular Dichroism
(VCD), Raman
Optical activity (ROA) and
Electronic Circular Dichroism (ECD) and these properties will be treated in
Chapter 11.
Another (magneto-)optical property, the 
term of
Magnetic Circular Dichroism (MCD) will be described in
Chapter 12.
Gauge-origin independent nuclear shieldings, magnetizabilities and rotational g tensors are obtained through the use of London atomic orbitals, and the theory is presented in several references [54,55,56,57]. Gauge-origin independent nuclear shieldings and magnetizabilities can also be obtained by using the the Continuous Transformation of the Origin of the Current Density method (CTOCD) approach [58,59,60]. In the present version of DALTON the CTOCD-DZ method is implemented and can be invoked by the keyword .CTOCD in the **PROPERTIES input module. More detailed information on CTOCD-DZ calculations can be found in section 10.9.1.
The indirect spin-spin couplings are calculated by using the triplet linear response function, as described in Ref. [61]. These are in principle equally simple to calculate with DALTON as nuclear shieldings and magnetizabilities. However, there are 10 contributions to the spin-spin coupling constant from each nucleus.10.1 Furthermore, the spin-spin coupling constants put severe requirements on the quality of the basis set as well as a proper treatment of correlation, making the evaluation of spin-spin coupling constants a time consuming task. Some notes about how this time can be reduced is given below.
Second Order Polarization Propagator Approximation (SOPPA) calculations [49,50,51,62,63] or SOPPA(CCSD) calculations [53,62,63] of the indirect spin-spin couplings, nuclear shieldings, magnetizabilities, rotational g tensors and the nuclear spin-rotation constants can be invoked by the additional keywords .SOPPA or .SOPPA(CCSD) in the **PROPERTIES input module. This requires for SOPPA that the MP2 energy was calculated by specifying the keyword .MP2 in the **WAVE FUNCTIONS input module, whereas for a SOPPA(CCSD) calculation the CCSD amplitudes have to be generated by specifying the keyword .CC in the **WAVE FUNCTIONS input module and .SOPPA(CCSD) in the *CC INPUT section. The use of London orbitals is automatically disabled in SOPPA calculations of the nuclear shieldings, magnetizabilities and rotational g tensors.