Thermal expansion and vibrational properties of α-Se and α-TeSe2 based on first-principles calculations

Based on the first-principles calculations, we investigated the thermal expansion and related vibrational properties of monolayer alpha-Se and binary compounds alpha-TeSe2. The effect of binary compounds on thermal expansion properties is explored theoretically. We find the two monolayers show totally positive thermal expansion from 0 to 500 K. The linear thermal expansion coefficients are close to each other below 300 K. However, they are 3.5 and 2.5 x 10(-5) K-1 for alpha-Se and alpha-TeSe2 at 500 K, showing much larger thermal expansion of the former. It can be attributed to the weaker Te-Se bond in alpha-TeSe2. Moreover, the phonon spectra, mode Gruneisen parameters, macroscopic Griineisen parameters, and the contributions of phonon modes to total thermal expansion at different temperature are investigated detailed, in order to explore the underlying physical mechanisms of thermal expansion.