Would be nice to have an option for Spinsys for SIMPSON

[jkshenton]

Expanding on issue raised by @AKM2022

[dch0ph]

Agreed. Being able to choose a set of atoms and write out the NMR parameters ready for a simulation is one of the key selling points. It fits naturally into a graphical programme since you you might well need to choose the spins interactively - indeed writing out whole unit cell would generally be a Very Bad Idea and should generate a warning.

Use cases:
Selecting an individual C atom + all the H atoms (including within adjacent molecules) within a certain radius, including the dipolar couplings.

Selecting atom X sites and writing them out. With multiple sites, you often would not want to include couplings and would generally construct the spectrum as a sum of single spin simulations.