BN的最低单重态-三重态激发能：聚合耦合团簇的观点
The lowest singlet-triplet excitation energy of BN: a converged coupled cluster perspective
摘要：
用高阶耦合团簇方法计算了BN双原子的$X ^3Π-a ^1Σ^+$激发能。收敛性已建立在1粒子基组和耦合集群扩展。明确列入连接四重激发$\hat{T}_4$是必要的，甚至半定量协议的限制值，而连接五重激发$\hat{T}_5$仍然有约60厘米$^{-1}$的影响。更高的激发仅占约10 cm $^{-1}$。在CCSDT水平上，包含内壳相关性进一步降低$T_e$约60 cm $^{-1}$，在CCSDTQ水平上降低85 cm $^{-1}$。我们的最佳估计，$T_e$ =183 $\pm$ 40 cm $^{-1}$，与早期的计算和实验非常一致，尽管具有较小的（和保守的）不确定性。BN的离解能（$X ^3Π$）为$D_e$ =105.74 $\pm$ 0.16 kcal/mol和$D_0$ =103.57 $\pm$ 0.16 kcal/mol。
英文摘要：
The notoriously small $X ^3Π-a ^1Σ^+$ excitation energy of the BN diatomic has been calculated using high-order coupled cluster methods. Convergence has been established in both the 1-particle basis set and the coupled cluster expansion. Explicit inclusion of connected quadruple excitations $\hat{T}_4$ is required for even semiquantitative agreement with the limit value, while connected quintuple excitations $\hat{T}_5$ still have an effect of about 60 cm$^{-1}$. Still higher excitations only account for about 10 cm$^{-1}$. Inclusion of inner-shell correlation further reduces $T_e$ by about 60 cm$^{-1}$ at the CCSDT, and 85 cm$^{-1}$ at the CCSDTQ level. Our best estimate, $T_e$=183$\pm$40 cm$^{-1}$, is in excellent agreement with earlier calculations and experiment, albeit with a smaller (and conservative) uncertainty. The dissociation energy of BN($X ^3Π$) is $D_e$=105.74$\pm$0.16 kcal/mol and $D_0$=103.57$\pm$0.16 kcal/mol.
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