Research Of Ionic Thermal Conductivity Using Molecular Dynamics: For Various Temperatures And Dimensions

Non-equilibrium molecular dynamics(NEMD)is widely used to calculate the thermal conductivity of various materials,but the influence of temperature gradient to thermal conductivity is received limited attention within current researches.By keeping the distance between the thermostats fixed,the temperature gradient is changed by changing the heat flux.The analysis of PDOS have shown that the larger temperature gradient activates more low-frequency vibrational modes which leads to larger thermal conductivities.Moreover,a new formula was derived to satisfactorily fit the thermal conductivities of bulk Si and silicon nanowires(Si NWs)for various cell sizes and the physical meaning of the formula was explained.It is shown that Stillinger-Weber(SW)potential and Tersoff potential of Si produce different thermal conductivities.By comparing first principles simulation's results,it can be seen that the Tersoff potential considered the effects of coordination number,which leads to better description of vibrational modes than SW potential.Last,by programming a code to calculate the phonon spectrum and velocities and lifetimes of phonons,the phonon properties of single-layer graphene and 3-layers graphene is analyzed.