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The phonon, elastic, and thermoelectric properties of Ti 2 CO 2 are investigated by first-principles calculations. The dynamic and mechanical stabilities of Ti 2 CO 2 are confirmed. The Ti 2 CO 2 monolayer exhibits strong acoustic-optical coupling with the lowest optical frequency of 122.83 cm -1 . The TA mode originates from the contribution of Ti(XY) vibrations and has the largest gruneisen parameter at the Γ point; the LA mode has the main contribution of O(XY) and Ti(XY) vibrations and has the lowest gruneisen parameter at the M point. The analysis of the phonon spectrum indicates that the vibration contributions from C, O, and Ti atoms are mainly located in the low-, middle-, and high-energy regions, respectively. The Seebeck coefficient and electronic conductivity increase with increasing carrier concentration under room temperature. The analysis of mechanical properties shows that Ti 2 CO 2 possesses a larger Young's modulus and bending modulus, which has a better ability to resist deformation. Thermal properties are further investigated., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

The modulation of electronic properties and quantum capacitance of Sc 2 CF 2 under a perpendicular external E-field was investigated using density functional calculations for the potential application of nanoelectronics and nanophotonics. Sc 2 CF 2 has an indirect band gap of 0.959 eV without an E-field. Furthermore, it undergoes a semiconducting-metallic transition under a positive E-field and a semiconductor-insulator transition under a negative E-field. The application of the negative E-field makes Sc 2 CF 2 have an indirect band gap. Sc-d, F-p, and C-p states are mainly responsible for the significant variation of the band gap. Sc 2 CF 2 under an external E-field always keeps the character of a cathode material under the whole potential. Especially, Sc 2 CF 2 under a negative external E-field is more suitable for the cathode material due to its much smaller | Q p |/| Q n | with much higher Q n . The charge analysis is further performed., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Functionalized MXenes have gained increasing interest in the fields of thermoelectric materials, hydrogen storage, and so forth. In this work, pressure-induced band modulation and optical properties of the Ti 2 CO 2 monolayer are investigated by using density functional theory with the hybrid (HSE06) functional. The calculation reveals that Ti 2 CO 2 MXenes under pressure are stable because of the positive E coh . Ti 2 CO 2 undergoes a semiconductor-to-metal phase transition at about 7 GPa. The metallization of Ti 2 CO 2 mainly results from the Ti-d state. Research indicates that there exist strong interactions between Ti-d and C-p, and Ti-d and O-p states, which are further confirmed by the charge analysis. In addition, the absorption is enhanced in the visible region with increasing pressure. We also observed some new absorption peaks in the visible region., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

Functionalized MXenes have wide applications in the fields of gas sensors, thermoelectric materials, and hydrogen storage. Strain-induced band engineering and the work function (WF) of Ti 2 CO 2 MXene are investigated theoretically. The calculations reveal that Ti 2 CO 2 MXenes are stable because of the negative E coh , and all the strains considered are within the elastic limit. For Ti 2 CO 2 MXene, strain-induced blue shift of the Ti d state results in the transformation from a semiconductor to a metal. At about 4%, Ti 2 CO 2 MXene transforms from an indirect band gap to a direct band gap. The decreased WF induced by the strain improves the power efficiency of Ti 2 CO 2 MXene., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)