In the present work, we consider electronic properties of WX₂ (X = S, Se) monolayers under a biaxial strain ${\epsilon }_b$ using the first principles study. Our calculations indicate that, at equilibrium, the WS₂ and WSe₂ monolayers are semiconductors with a direct band gap of respectively 1.800 eV and 1.566 eV while their bulk structures are indirect semiconductors. The electronic properties of the WX₂ monolayers are very sensitive with the biaxial strain, especially compression strain. The biaxial strain ${\epsilon }_b$ is the cause of the band gap of the WX₂ monolayers and especially the semiconductor–metal phase transition has occurred in the WS₂ monolayer at ${\epsilon }_b=-10\%$. In addition, the direct–indirect band gap transition was observed in both WS₂ and WSe₂ monolayers at a certain elongation of biaxial strain ${\epsilon }_b$. The phase transitions in these monolayers can be very useful for their applications in nanoelectromechanical devices.

在目前的工作中，我们考虑了双轴应变下WX ₂（X = S，Se）单层的电子性质${\epsilon }_b$使用第一原理研究。我们的计算表明，在平衡状态下，WS ₂和WSe ₂单层是直接带隙分别为1.800 eV和1.566 eV的半导体，而它们的本体结构是间接半导体。WX ₂单层的电子性质对双轴应变（尤其是压缩应变）非常敏感。双轴应变${\epsilon }_b$是WX ₂单层带隙的原因，尤其是在WS ₂单层中发生了半导体-金属相变${\epsilon }_b=--10％$。此外，在一定的双轴应变伸长率下，在WS ₂和WSe ₂单层中都观察到了直接-间接带隙跃迁${\epsilon }_b$。这些单层中的相变对其在纳米机电装置中的应用非常有用。