Here, we investigated high-pressure behaviors of four end-members of K-Na-Ca-Mg alkali-bearing double carbonates (K₂Mg(CO₃)₂, K₂Ca(CO₃)₂, Na₂Mg(CO₃)₂, and Na₂Ca(CO₃)₂) using first-principles calculations up to ~ 25 GPa. For K₂Mg, K₂Ca, and Na₂Mg double carbonates, the transitions from rhombohedral structures (R \(\stackrel{\mathrm{-}}{3}\) m or R \(\stackrel{\mathrm{-}}{3}\)) to monoclinic (C2/m) or triclinic (P \(\stackrel{\mathrm{-}}{1}\)) structures are predicted. While for Na₂Ca(CO₃)₂, the P2₁ca structure remains stable across the calculated pressure range. But the high-pressure behavior of Na₂Ca double carbonate has changed over 8 GPa: the b-axis becomes more compressible than a-axis; [CO₃] –I groups tilt out of the a-b plane upon compression and reverse the direction of rotation at 8 GPa. The parameters for the equations of state of these minerals and their high-pressure phases were all theoretically determined. The predicted transformation is driven by the differences in the compressibility of structural units. The K⁺ and Na⁺ coordination polyhedra are more compressible in the structure, compared with the high axial rigidity of C–O bonds in the [CO₃] triangle along the a-b plane. Our results provide projections of the high-pressure behaviors of trigonal double carbonates, in part by helping to clarify the relation among the average metallic ionic radius (R_avg), the bulk modulus (K₀), and the transition pressure (P_T). The transition pressure (P_T) is anticorrelated to the average metallic ionic radius (R_avg), and a larger R_avg results in a lower bulk modulus (K₀) for the trigonal double carbonates. Furthermore, alkali-bearing double carbonates found as inclusions in the natural diamond may indicate a hydrous parental medium composition and a deeper genesis mechanism.

_{在这里，我们研究了 K-Na-Ca-Mg 含碱双碳酸盐的四个端元 (K 2} Mg(CO ₃ ) ₂、K ₂ Ca(CO ₃ ) ₂、Na ₂ Mg(CO )的高压行为。₃ ) ₂和 Na ₂ Ca(CO ₃ ) ₂ ) 使用最高约 25 GPa 的第一性原理计算。对于 K ₂ Mg、K ₂ Ca 和 Na ₂ Mg 双碳酸盐，从菱面体结构的转变（R \(\stackrel{\mathrm{-}}{3}\) m或R \(\stackrel{\mathrm{ -}}{3}\)) 到单斜 ( C 2/ m ) 或三斜 ( P \(\stackrel{\mathrm{-}}{1}\) ) 结构被预测。而对于 Na ₂ Ca(CO ₃ ) ₂，P 2 ₁ ca结构在计算的压力范围内保持稳定。_{但是 Na 2} Ca 双碳酸盐的高压行为在超过 8 GPa 时发生了变化： b轴变得比a轴更易压缩；[CO ₃ ] –I 组倾斜出a - b压缩平面并在 8 GPa 时反转旋转方向。这些矿物的状态方程及其高压相的参数都是理论上确定的。预测的变换是由结构单元的可压缩性差异驱动的。与沿ab平面的 [CO ₃ ] 三角形中 C-O 键的高轴向刚度相比，K ⁺和 Na ^{+配位多面体在结构中更具可压缩性。}我们的结果提供了对三角双碳酸盐高压行为的预测，部分有助于阐明平均金属离子半径 ( R _avg )、体积模量 ( K ₀) 和过渡压力 ( P _T )。过渡压力 ( P _T ) 与平均金属离子半径 ( R _{avg ) 反相关，} R _avg越大，三角双碳酸盐的体积模量 ( K _{0 ) 越低。}此外，在天然钻石中作为内含物发现的含碱双碳酸盐可能表明含水母介质成分和更深层次的成因机制。