用紧束缚理论研究压力对固体能带结构的影响

Using the Tight-binding Theory to Study the Influences of Pressure on the Energy Band Structure of a Solid

应用紧束缚理论,计算了体心立方结构1s能带和2s能带,讨论了外界压力对能带结构的影响。研究结果表明,压力使固体的晶格常数发生变化,导致体心立方晶格的1s和2s能带的宽度以及两带之间的禁带宽度发生变化。利用所得结果,具体计算了外界压力对锂金属能带结构的影响, 在晶格常数附近, 随着压力的增大, 锂金属的1s和2s能带将变宽,两带之间禁带宽度将变小,理论计算结果与实验观察结果在数量级上是一致的。

Various external factors can influence on the energy-band structure of a solid, the changes of the energy -band structure will result in many novel physical phenomena, which has made people explore many new applied fields and attracted considerable attention in the last several decades. In the middle of the 70's of the 20 th century, the influences of pressure on the absorption band edge of the semiconductor GaAs have been observed in the experiment. In the early period, some theoretical methods have been developed to investigate dependence of the direct energy gap of GaAs on hydrostatic pressure and optical properties of semiconductors under pressure. Although these theoretical methods have achieved some successes, yet they belong basically to the semi-experience phenomenology and the semi-classical theory. Recently, by using self-consistent pseudopotential method based on density-functional theory, XIAO Qi, et al. have investigated the electronic structure of iron pyrite FeS 2 under external pressure, it was shown that the forbidden-band width become wider with increase of external pressure. However, the work studying the influence of external pressure on the energy-band structure by using energy-band theory of quantum mechanics is little still. The aim in the paper is to study the influences of pressure on the energy-band structure of a solid by using the tight-binding theory. We have calculated the 1s and 2s energy bands of a body-centered cubic lattice, and discussed the influences of pressure on the energy-band structure. The results show that the pressure makes lattice constant change, which results in the changes of the 1s and 2s energy-band width and the forbidden-band width between two energy bands for the body-centered cubic lattice. From our results, we have calcu- lated concretely the influences of pressure on the energy-band structure of the Li metal, with the increase of the pressure, the 1s and 2s energy-band width of Li metal will widen, the forbidden-band width between the two energy bands will narrow. Compared with the published data, our results are agreement with the experiment results in order of magnitude. In summary, by using the tight-binding theory we have investigated the influence of pressure on the energy- band structure of a solid. We can describe the energy-band width and the forbidden-band width as a function of the distance between neighbour atoms, when the pressure increase, the distance between neighbour atoms will decrease and make the energy-band structure of a solid change, which makes people understand easily the physical essence of the influence of pressure on the energy-band structure of a solid, it is obvious that the tight-binding theory has remarkable advantages in studying the influence of pressure on the energy-band structure of a solid.