Spin crossover (SCO) complexes are functional materials that exhibit a change in spin state from low-spin (LS) to high-spin (HS), or vice versa, as a function of external stimuli like temperature, pressure, short magnetic pulses, pH, or light. As a result, SCO complexes are promising for molecular spintronics, memory devices, displays, sensors, optical devices, conductors, and terahertz technology. SCO behavior is typically observed in 3d transition metal complexes (TMCs) with electronic configurations ranging from d 4 to d (e.g., Mn(II/III), Fe(II/III), Co(II/III), , and Ni(II) ). Of these, Fe(II) SCO complexes with nitrogen-coordinating ligands have been designed and studied most extensively because they exhibit the greatest structural differences between HS and LS states. This is advantageous since it allows for clear differentiation between the two states and leads to better switching properties in molecular memory devices. To identify if a material has suitable SCO properties (i.e., a clear, well-defined spin transition at a specific temperature), numerous experimental techniques are used to characterize the material. Magnetic susceptibility measurements as a function of temperature are the most common experimental means to observe SCO behavior and reveal the transition temperature (T1/2), i.e., the temperature at which the spin transition takes place. Mössbauer spectroscopy carried out at variable temperature may also be used to characterize Fe(II) SCO complexes by determining the spin states of complexes in a sample. In addition, X-ray crystallography is used to characterize SCO transitions that are accompanied by a change in the complex structure. Other spectroscopic methods such as variable-temperature nuclear magnetic resonance (NMR), infrared (IR), Raman, and UV/Vis are also employed in the characterization of SCO behavior. The SCO behavior of a complex is influenced by its parameters to recover exact conditions do not necessarily have improved agreement with experimental data. However, results from range-separated hybrids with parameters tuned based on CASPT2 agree better with both CASPT2 and experiments. There is generally not a widespread agreement about which DFT functionals perform best for SCO properties, even if we restrict ourselves to a fixed metal and oxidation state, such as Fe(II).