The D_5h →D_10h isomerization in the C₁₀ carbon cluster is investigated at the relativistic, all-electron CCSDT(Q)/CBS level. Previous high-level studies examined this isomerization at the valence CCSD(T)/CBS level. We show that capturing this isomerization energy requires accurate treatment of the CCSD(T)/CBS, post-CCSD(T), core-valence, scalar relativistic, diagonal Born–Oppenheimer, and zero-point vibrational energy components. Combining these components shows that the two structures are practically isoenergetic at 0 K (i.e., the D_5h structure is more stable by merely +0.100 kcal mol^–1). We also show that computationally economical composite protocols erroneously predict that the D_10h structure is energetically more stable at 0 K.

在相对论全电子CCSDT（Q）/ CBS水平下研究了C ₁₀碳簇中的D _5h →D _10h异构化。先前的高级研究在价CCSD（T）/ CBS级别上检查了这种异构化。我们表明，捕获这种异构化能量需要对CCSD（T）/ CBS，后CCSD（T），核价，标量相对论，对角Born–Oppenheimer和零点振动能分量进行精确处理。组合这些成分可以看出，这两个结构在0 K时实际上是等能量的（即，D _5h结构仅+0.100 kcal mol ^–1才更稳定）。我们还表明，计算上经济的复合协议错误地预测了D _10h 在0 K时，结构在能量上更加稳定。