The nonadiabatic coupling terms (NACTs, F_ij’s) between triplet electronic states can be well approximated with a very simple equation suggested recently [J. Chem. Phys . 146, 064107 (2017)], using only adiabatic potential energies ($V_i^a$ and $V_j^a$). Furthermore, the second-order differentiation can be evaluated accurately from the energy gaps, $(V_i^a-V_j^a)$, at just three consecutive geometries, even at a point exhibiting severe singularity in the behaviour of NACTs. The performance of this approximation method was investigated for the couplings between the 3³Π$3^3\mathrm{\Pi }$ and 4³Π$4^3\mathrm{\Pi }$ states of NaK, between the 1³B_3u$1^3{B}_{3u}$ and 2³B_3u$2^3{B}_{3u}$ states of N₂, and between the 2³A^″$2^3{A}^{″}$ and 3³A^″$3^3{A}^{″}$ states of methylene (CH₂).

三重态电子态之间的非绝热耦合项（NACT，F _ij）可以用最近提出的一个非常简单的方程很好地近似[ J. Chem。物理学。146，064107（2017）]，仅使用绝热势能（${\mathrm{伏特}}_{\mathrm{一世}}^{\mathrm{一个}}$ 和 ${\mathrm{伏特}}_{Ĵ}^{\mathrm{一个}}$）。此外，可以从能隙中准确评估二阶微分，$（{\mathrm{伏特}}_{\mathrm{一世}}^{\mathrm{一个}}--{\mathrm{伏特}}_{Ĵ}^{\mathrm{一个}}）$，即使在三个连续的几何图形上，甚至在NACT的行为表现出非常奇异的点上也是如此。这种近似方法的性能进行了研究用于之间的联接器3 ³ Π$3^3\mathrm{\Pi }$和4 ³ Π$4^3\mathrm{\Pi }$在1 ³ B _3u之间的NaK状态${\mathrm{1个}}^3{乙}_{3ü}$和2 ³ B _3u${\mathrm{2个}}^3{乙}_{3ü}$N _2的状态，以及2 ³ A ^”之间的状态${\mathrm{2个}}^3{\mathrm{一个}}^{\text{'}\text{'}}$和3 ³ A ^''$3^3{\mathrm{一个}}^{\text{'}\text{'}}$亚甲基（CH ₂）的状态。