Substances with a complex electronic structure exhibit non-Drude optical properties that are challenging to interpret experimentally and theoretically. In our recent paper [Phys. Rev. E 105, 035307 (2022)2470-004510.1103/PhysRevE.105.035307], we offered a computational method based on the continuous Kubo-Greenwood formula, which expresses dynamic conductivity as an integral over the electron spectrum. In this Letter, we propose a methodology to analyze the complex conductivity using liquid Zr as an example to explain its nontrivial behavior. To achieve this, we apply the continuous Kubo-Greenwood formula and extend it to include the imaginary part of the complex conductivity into the analysis. Our method is suitable for a wide range of substances, providing an opportunity to explain optical properties from ab initio calculations of any difficulty.