The thermal and optical properties of layered structures of molybdenum disulfide (MoS₂) were studied based on the first-principles density functional theory. The phonon density of states in various layered and bulk MoS₂ shows a discontinuous band gap between about 7.0 and 8.0 THz. The specific heat variation with temperature and other thermodynamic properties like the Helmholtz free energy, entropy, and total energy are similar between the layered structures and bulk MoS₂. The specific heat increases rapidly with increasing temperature in the region < 500 K and nearly flattens when the temperature goes above 1000 K. For the temperature < 400 K, the electronic plus vibrational Helmholtz free energy is positive, indicating electrons can be easily restricted to the MoS₂ layers. The layered structures affect the optical properties in both in-plane and through-plane substantially. The monolayer has the lowest values of the dielectric function, optical conductivity, and absorptive index, whereas the bulk material shows the highest ones correspondingly. For the real refractive index, the monolayer has the lowest value at the low energy level, but could go to the highest in the interval from 15.0 eV to 35.5 eV or exceeding 37.6 eV. The band gap of the layered structures generally decreases with increasing layer number. The calculated band gap for the MoS₂ bilayer at 1.78 eV matches with the experimental measurement in the literature.

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二硫化钼的热和光学性质的第一性原理计算

基于第一原理密度泛函理论研究了二硫化钼（MoS ₂）层状结构的热学性质和光学性质。在各种分层的和块状的MoS ₂中，声子的态密度显示出大约7.0和8.0 THz之间的不连续带隙。层状结构和块状MoS ₂之间的比热随温度和其他热力学性质（如亥姆霍兹自由能，熵和总能）的变化相似。当温度<500 K时，比热随温度的升高而迅速增加，当温度超过1000 K时，比热几乎趋于平坦。对于温度<400 K，电子加振动亥姆霍兹自由能为正，表明电子可以很容易地限制在硫化钼₂层。层状结构实质上影响面内和贯通面的光学特性。单层具有最低的介电功能，光导率和吸收指数，而块状材料相应地表现出最高的值。对于真实折射率，单层在低能级下具有最低值，但在15.0 eV至35.5 eV或超过37.6 eV的范围内可能达到最高。层状结构的带隙通常随着层数的增加而减小。MoS ₂双层在1.78 eV处的计算带隙与文献中的实验测量值相符。