Vibration Of Hexagonal Boron Nitride

Hexagonal boron nitride(h-BN)is a kind of two-dimensional layered nanomaterial with excellent mechanical,optical,electrical and thermal properties and possess an expecting application prospect in composite materials,photoelectricity,heat exchange,and so on.The vibrational characteristics of h-BN are studied through molecular dynamics simulation,continuum plate model and density-functional tight-binding method in the thesis.(1)Molecular dynamics simulation is implemented to calculate the bending stiffness and Poisson’s ratio and the influence of temperature,size and initial stress on the thermal vibration of single-layered h-BN are studied.The theoretical results of Kirchhoff plate model are compared with the results of the molecular dynamics and it can predict the vibrational behavior of h-BN with four edge-clamped boundary conditions well.The results obtained by molecular dynamics simulation show the first four natural frequencies of h-BN change linearly and the first natural frequency decreases with the increase of electric field intensity along the polarization direction.The natural frequencies keep decreasing with the increase of electric field intensity along both positive and negative non-polarization direction,while the natural frequency of h-BN increases with the increase of electric field intensity along both positive and negative transverse electric field.The natural frequencies change significantly when the direction of electric field is within 45 degrees to 90 degrees.(2)The van der Waals interaction coefficient of double-layered h-BN is obtained using molecular dynamics simulation and theoretical analysis.The simulation is carried out to analyze the influence of stacking types.It is found that the natural frequency of AA’ and AA is minimal than other types.The vibration of double-layered h-BN exists inphase and antiphase vibration.The antiphase frequency is obviously larger than the inphase one.The double-layered Kirchhoff plate model with springs can predict the vibrational behavior of double-layered h-BN.(3)Based on density-functional tight-binding method,the structure of single-layered h-BN is analyzed.It is found that the B-N bonds show strong polarity and the structure has obvious edge effect.The bending stiffness and Poisson’s ratio of h-BN are calculated.The effect of size and initial stress on the thermal vibration of single-layered h-BN is studied and its results agree well with the results of molecular dynamics simulation.It is found that the Tersoff potential,although simplified in the polarity of B-N bonds,can accurately reflect the mechanical properties and vibrational characteristics of h-BN.