Nuclear Magnetic Resonance (NMR) is an atomic-level method for structure determination in systems ranging from small molecules to large proteins. Calculations of NMR parameters can support interpretation, assignment, and prediction of the NMR spectra.1 13C NMR applies to most of organic and biological compounds, covalent-organic and metal-organic frameworks, etc. For diamagnetic systems, it is still demanding for the theoretical calculation of ever-larger system with ever-greater precision.2 For paramagnetic systems, the presence of unpaired electron(s) further complicates the NMR study both experimentally and computationally.3 In this talk, I will show a joint experimental and Density Functional Theory (DFT) study of paramagnetic NMR for Cu(II) complexes,4–6 as well as a demonstration of using the eXtended ONIOM method2,7 with DFT for calculating 13C NMR shifts for large diamagnetic molecules.