In binary neutron star (BNS) mergers, the radioactive decay of freshly synthesized heavy elements produces emissions in the ultraviolet-optical-infrared range, giving rise to a transient called a kilonova. The kilonova is an excellent probe to understand the origin of elements heavier than iron. The observational properties of the kilonova (light curve and spectra) depend on the bound-bound opacity of the heavy elements. Hence, a detailed opacity is necessary to model the realistic kilonova light curve and spectra. However, such calculations for opacity, and correspondingly, the realistic light curve, were largely unavailable, especially for the condition suitable at an early time (t < 1 day).
In my talk, I will discuss recent developments and challenges in modelling kilonova light curves. Also, I will share my recent work on opacity and light curve calculations of the kilonova, focusing on early time (t < 1 day).