First-principles Calculations Of Phonon Spectrum And Thermodynamic Properties Of AlN

Nitride has important applications in many areas because of physical and the structural advantages. AIN materials have high thermal conductivity, low coefficient of thermal expansion, high hardness, non-toxic, excellent dielectric properties and chemical stability so that it has a wide and many potential uses. Therefore, the paper " AIN crystal phonon vibration spectra and thermal properties computing" has important theoretical significance and value.In this paper, we study the AIN phonon spectra and thermodynamics and present the results of theoretical calculations. First, In considering the calculation accuracy and computational efficiency, we carry a parameter test of the AIN crystal ecut and kopints, then ecut taken as50Hartree (1361eV), kpoint taken as6×6×6. On this basis,We obtain the phonon spectrum of AIN crystals, and the relationship of internal energy, heat capacity, entropy and free energy with temperature, through the use of the Density Functional Theory, first-principles, ABINIT software in the Linux operating system. Also, we theoretically analyze the relationship. The results of calculations show that,(1) the12curves that AIN crystal have and which form a optical band gap together, three curves relate to branches acoustic wave and nine curves are branches optical wave. Furthermore, as the temperature rises, the calculations also reveal that (2) the internal energy of AIN crystals increases,from20k to200k, the internal energy slow growth, and then the internal energy almost linearly increases as the temperature increases;(3) the heat capacity increases rapidly, and then gradually approaches to steady state;(4) the entropy increases and the relationship has a certain bending;(5) the free energy decreases, the curve of free energy and the temperature is concave to the downward. The calculation results presented in this paper are in consistent with the laws of physics.After the above research, which can provide theoretical guidance and practical applications for future research。...