An empirical molecular mechanics force field has been built for the [Fe(pyrazine)][Ni(CN)4] spin crossover complex using Raman spectroscopic and nuclear inelastic scattering data. Based on this force field, molecular dynamics simulations were conducted to investigate the lattice dynamical properties of the complex in the high-spin and low-spin states. The extracted thermodynamic and mechanical parameters match well with the corresponding experimental data. Most importantly, the force field can successfully reproduce the low-frequency acoustic part of the partial densities of vibrational states, which is vital for the understanding the thermodynamic analysis of the spin crossover phenomenon in crystalline solids and which would be difficult to tackle by quantum mechanical methods.