The spin crossover (SCO) phenomenon is among the most complicated second-order transitions to be modelled from first principles. Some ad hoc strategies have been successful for modelling solution SCO, but this is rare for solid state SCO because of the added complexity coming from (a) interacting molecules and (b) packing effects. In this study, the solid state SCO transition of solvent-free crystalline [CoII(dpzca)2] is modelled through the calculation of the transition temperature (T1/2) under a range of different physical conditions. This candidate complex undergoes both thermal and pressure-activated SCO (quoted T1/2 values obtained at γHS = 0.5): from pressures of 1 to 2100 bar, the SCO is mostly abrupt (gradual:abrupt = 20 : 80; 173 K 2500 bar is likely due to a crystal transition or phase change of the HS [CoII(dpzca)2] unit cell, as the only available crystallographic data in this pressure range (LS [CoII(dpzca)2] at 4300 bar) are in excellent agreement with the computed ones.