Abstract: The McMillan formula is a crucial component of BCS superconductivity theory and a vital tool for predicting the superconducting transition temperature in conventional superconductors. This paper introduces the original McMillan formula and its Allen-Dynes modified version. Using hydrogen-based superconductor as example, we apply the McMillan equation to reveal the relationships between electron-phonon coupling strength, logarithmic phonon frequency, and superconducting transition temperature. Superconductivity and its electronic properties represent significant challenges and frontier topics in solid-state physics. Teaching solid-state physics should emphasize superconductivity-related issues and their role in modern physics.

Key words: superconducting transition temperature, hydrogen-based superconductors, electron-phonon coupling