The straight chain n-alkanes and their mixture,which can be used as phase change materials (PCM) for thermal energy storage,have attracted much attention in recent years.We employ the molecular dynamics (MD) simulation to investigate their thermophysical properties,including self diffusion and melting of n-octadecane with crystal and amorphous structures.Our results show that,although the initial and melted structures of n-octadecane with crystal and amorphous are different,the melting behaviors of n-octadecane judged by the self diffusion behavior are consistent.The MD simulation indicates that both the crystal and amorphous structures are effective for the property investigation of n-octadecane and the simulated conclusion can be used as reference for modeling the alkanes-based PCM system.