Norsethite, BaMg(CO3)2, is a mineral with a structure analogous to dolomite, CaMg(CO3)2, which can be readily synthesized at room temperature. Therefore, norsethite and other carbonates with a norsethite structure have been used to investigate the possible formation mechanisms of dolomite under ambient conditions. In this work, the crystal structures of dolomite, norsethite, and norsethite-like structures (i.e., PbMg(CO3)2, SrMg(CO3)2, and the newly proposed structure of RaMg(CO3)2) have been studied at an atomic scale by means of calculations based on density functional theory (DFT). The energies of these carbonates and precursors calculated have been compared to obtain the relative energies of these double carbonates. We found that norsethite and RaMg(CO3)2 have the lowest relative energies, indicating that these phases must be relatively easy to synthesize under ambient conditions. Differently, PbMg(CO3)2, SrMg(CO3)2, and dolomite, have much higher relative energies, indicating that their synthesis is more difficult. Our calculations are consistent with the results of the synthesis experiments reported to date. Furthermore, our theoretical results open the door to future experimental works on the synthesis of double carbonates aimed at obtaining RaMg(CO3)2 and SrMg(CO3)2.