Paliwal Uttam, Tanwar Pradeep, Joshi K B
Department of Physics, Jai Narain Vyas University, Jodhpur, 342011, India.
Department of Physics, ML Sukhadia University, Udaipur, 313001, India.
J Mol Model. 2024 Feb 22;30(3):80. doi: 10.1007/s00894-024-05865-9.
In this work the first-principles calculations of the structural, electronic and thermoelectric properties of monolayer TiSe are presented. The optimized lattice parameter of monolayer TiSe shows excellent agreement with the experimental value. The computed band structure and density of states calculations predict metallic nature of monolayer TiSe with overlapping of 0.44 eV between the lowest conduction band and top valance band at high symmetry point M. The position of pseudogap formed by Ti-3d orbitals near the Fermi level confirms the mechanical stability of monolayer TiSe. Due to the influence of positive strain (tensile strain), the Ti-Se bond length increases and the layer height decreases. The applied tensile strain changes the metallic nature of TiSe into a semiconductor with opening of bandgap. It has also been observed that the positions of conduction band minima and valance band maxima change with strain. The charge analysis shows that charge transfer from Ti to Se atom increases when tensile strain is applied, while an opposite trend is observed with compression. The computed thermoelectric coefficients i.e. Seeback coefficient, power factor and figure of merit are in good agreement with the experimental data. The temperature dependence of these coefficients is also reported.
The density functional theory based calculations are reported employing the PBE-GGA ansatz using the plane wave-pseudopotential method embodied in the Quantum ESPRESSO package. The self-consistent field calculations are performed over a dense Monkhorst-Pack net of 12 × 12 × 1 k-points. The energy convergence criteria for the self-consistent field calculation were set to 10 Ry/atom with a cutoff energy of 90 Ry. The thermoelectric properties are computed by combining the band structure calculations with the Boltzmann transport equation using Boltztrap2 peckage.
在本研究中，我们给出了单层TiSe结构、电子和热电性质的第一性原理计算结果。单层TiSe的优化晶格参数与实验值吻合良好。计算得到的能带结构和态密度表明，单层TiSe具有金属性，在高对称点M处，最低导带与最高价带之间的重叠为0.44 eV。费米能级附近由Ti-3d轨道形成的赝能隙位置证实了单层TiSe的力学稳定性。由于正应变（拉伸应变）的影响，Ti-Se键长增加，层间距减小。施加的拉伸应变使TiSe的金属性转变为具有带隙的半导体。还观察到导带最小值和价带最大值的位置随应变而变化。电荷分析表明，施加拉伸应变时，电荷从Ti原子转移到Se原子的量增加，而压缩时则观察到相反的趋势。计算得到的热电系数，即塞贝克系数、功率因子和优值与实验数据吻合良好。还报道了这些系数的温度依赖性。
采用基于密度泛函理论的计算方法，使用Quantum ESPRESSO软件包中体现的平面波赝势方法，采用PBE-GGA近似。自洽场计算在12×12×1的密集Monkhorst-Pack k点网格上进行。自洽场计算的能量收敛标准设置为10 Ry/原子，截止能量为90 Ry。热电性质通过使用Boltzmann transport equation结合能带结构计算和Boltztrap2软件包进行计算。
