Evolution of the chemical composition at the center of the white dwarf as a function of temperature for different ¹²C+¹²C rates: CF88 rate (top left), LER-1.5-0.1-1.0 model (top right), and α/p: LER-1.5-0.1-5.0 with α/p = 5.0 (bottom left), and LER-1.5-0.1-0.2 with α/p = 0.2 (bottom right). To improve the readability, the upper limit to the vertical axis has been set at a mass fraction of 0.01, hence the curves of ¹²C and ¹⁶O (both with mass fractions  > 0.1) lie out of the plot (the relative variations in their mass fractions are very tiny within the temperature range shown). The thick curve gives the electron molar fraction. The abundance of ²³Ne reflects the amount of electron captures on ²³Na: it grows quickly with increasing temperature at low temperatures but levels out at T ~ 5.5 × 10⁸ K for the CF88 model and T ~ 3.5 × 10⁸ K for the rest of the models shown. The sum of the abundances of ¹⁷O and ¹⁴C reflect the electron captures on ¹³N: the sum grows steadily but is always smaller than the abundance of ²³Ne, except at very high temperatures. The top axes of the plots belonging to models CF88 and LER-1.5-0.1-1.0 are labeled with the time to runaway.