The mandatory attributes of the interaction_term CT include interaction kind (strictly from one of the following: shielding, shift, gtensor, hfc, quadrupolar, exchange, jcoupling, dipolar, spinrotation,

zfs), interaction identifier (an integer), physical units and the identifier of at least one spin to which the interaction relates. The second spin (for binary interactions) and a text label are optional. Thiazovivin in vivo We will not discuss here the relative merits of the different styles of specifying eigenvalues – they have a long history [1], [2], [3], [4], [6], [7], [21], [22], [23], [24], [25] and [26] and a proper unification of the existing conventions is only possible in a format that includes all of them as options.

This puts some strain on the software developer (a SpinXML parser should be able to interpret all conventions listed in Fig. 1), but makes life easier for the end user. When an instance of SpinXML is being written rather than parsed, we would join IUPAC [4] and [7] in recommending the 3 × 3 matrix style for spin interaction tensor specification. As a matter of practical safety, we would not recommend specifying dipolar interactions as 3 × 3 interaction matrices or [eigenvalue data] + [orientation data] pairs: there are quite a few papers in Magnetic Resonance literature where the listed dipole–dipole coupling constants or matrices do not correspond to a physically possible arrangement of particles in 3D space. We recommend recording inter-nuclear Venetoclax clinical trial and inter-electron dipolar couplings by specifying particle coordinates. Electron–nuclear dipolar couplings should be supplied as anisotropic hyperfine interactions that naturally incorporate the case of an electron–nucleus pair with a delocalized electron. The case of two spatially proximate delocalized electrons is covered by exchange and zero-field splitting. If the above does not apply and dipole–dipole couplings still

have to be specified as effective spin interactions (this may be necessary in strongly non-Born–Oppenheimer systems where nuclei are delocalized), care should be taken BCKDHA to ensure that the numbers provided are consistent with a physically possible set of particle coordinates. Another problematic area is the difference between chemical shielding and chemical shift, and the associated debate [1], [2] and [3] about the definition of span and skew parameters – electronic structure theory calculations report absolute nuclear shielding defined in terms of molecular energy derivatives [3], whereas experimental data is reported as fractional frequency shifts relative to a specific substance [2].