Molecular Dynamics and Transfer Integral Investigations of an Elastic Anharmonic Model for Phonon-Induced Spin Crossover

Based on a vibronic description of the spin-crossover (SC) molecule, the electronic and elastic properties of a chain of anharmonically coupled SC molecules are studied by means of transfer integral (TI) and molecular dynamics (MD) simulations. The thermodynamical properties (high spin fraction and lattice deformation) are derived and show the existence of a first-order transition driven by the phonon field. The MD investigations of the velocity autocorrelation function evidenced that the density of phonon states shows a redshift and a broadening at high temperature, attributed to the enhancement of the phonon entropy. This result is discussed in relation to the thermal dependence of the dispersion relation ω(q) and that of the effective intermolecular elastic constant.