Density grids of BH-star binaries using our rapid population synthesis code StarTrack (red color) and detailed stellar evolution code MESA (blue color) from Xu et al. (in prep.). The black points are StarTrack BH-star systems that later evolve into BH–BH mergers via the SMT subchannel. The upper panels show the grid for our default StarTrack model. The bottom panels are results for the StarTrack model with 100% nonconservative mass transfer and no natal kick due to asymmetric mass ejection (except neutrino emission). The left panels are for StarTrack models with 1% solar metallicity, and the right panels are for 10% solar metallicity. The detailed grid is for 10% solar metallicity.