First-principles calculations on electronic, superconducting, mechanical, and thermodynamic properties for the superhard compound Tc2C under pressure

Abstract

This study presents a theoretical investigation on the electronic, superconducting, mechanical, and thermodynamic properties of the superhard compound Tc2C up to 100 GPa. The investigation is conducted via the first-principles plane-wave pseudopotential method. Furthermore, to treat the exchange-correlation potential for the total energy calculations, the revised Perdew–Burke–Ernzerhof formulation stemming from the generalized gradient approximation is employed. The results suggest that Tc2C is a potential hard compound due to the robust covalent bonding between Tc and C atoms. Moreover, the electronic structure and electron–phonon coupling reveal that Tc2C is a superconducting material with Tc of 0.59 K at 0 GPa. Additionally, using the quasi-harmonic Debye model, the variation of crucial structural parameters, such as the volume thermal expansion coefficient, heat capacity, and isothermal bulk modulus and its pressure derivatives, is predicted in terms of temperature and pressure. The results demonstrate that temperature and pressure have contrasting effects on the volume thermal expansion coefficient and heat capacity, and the effect of temperature is larger than that of pressure, especially at low temperatures. The isothermal bulk modulus decreases with increasing temperature but increases with increasing pressure. The first and second pressure derivatives of the isothermal bulk modulus for Tc2C are not the assumed constants in the equation of state study at high pressures and temperatures. To our knowledge, this study presents the first quantitative theoretical prediction of the pressure and temperature dependence of the thermodynamic parameters for Tc2C, which is essential for understanding the basic physical properties of similar transition metal carbides.