I was trying to replicate a paper (Bao et al., Solar Energy Materials and Solar Cells 168 (2017) 78–84) in Lumerical. Random media of TiO2 with volume fraction 0.4 and radius 0.5 micrometre. The structure span 4*4*10 micrometre. The reflection I am getting similar but the sum of R+T is not equal to 1. Since media is lossless so there is no chance of absorption. I tried different things such as changing the mesh size, changing the position of the source and monitor but there is no change in the result at all. I also tried to replicate some experimental work on TiO2 random media. But again R+T is not equal to 1 and R is giving lesser than whatever reported in the paper. I have attached the results obtained from the simulation and reported in the paper (Bao et al. 2017).
One thing which I want to mention
that when I did the simulation of similar random media for smaller thicknesses such as 1 or 2 micrometres then R+T is giving 1. But as thickness increases, T approaches zero.