Grids of NAUTILUS models with varying temperature and hydrogen nuclei density. Each plot shows the contour levels of the N₂H⁺ (top left), N₂D⁺ (top middle), DNC (bottom left), and DCN (bottom middle) abundances; the N₂H⁺ deuterium fraction (top right); and the DNC/DCN ratio (bottom right) at time t ≈ 10⁶ yr. Additionally, we show the contours that correspond to the abundances derived from the N₂H⁺, N₂D⁺, DNC, and DCN column densities in TMC 1-C (black) and TMC 1-CP (white), their uncertainties (dashed lines), and the upper bound values if present (white arrows). The model does not reproduce our estimated DNC/DCN ratio towards TMC 1-C, and thus the black contours are missing from that panel.