Dynamical consideration that goes beyond the common Born–Oppenheimer approximation (BOA) becomes necessary when energy differences between electronic potential energy surfaces become small or vanish. One of the typical scenarios of the BOA breakdown in molecules beyond diatomics is a conical intersection (CI) of electronic potential energy surfaces. CIs provide an efficient mechanism for radiationless electronic transitions: acting as “funnels” for the nuclear wave function, they enable rapid conversion of the excessive electronic energy into the nuclear motion. In addition, CIs introduce nontrivial geometric phases (GPs) for both electronic and nuclear wave functions. These phases manifest themselves in change of the wave function signs if one considers an evolution of the system around the CI. This sign change is independent of the shape of the encircling contour and thus has a topological character. How these extra phases affect nonadiabatic dynamics is the main question that is addressed in this Account.

中文翻译：

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圆锥形交叉口非绝热动力学中的几何相位效应

当电子势能面之间的能量差变小或消失时，超越常规的Born-Oppenheimer逼近（BOA）的动力学考虑就变得很有必要。BOA在双原子以外的分子中分解的典型情况之一是电子势能面的圆锥形交点（CI）。CI为无辐射电子跃迁提供了一种有效的机制：充当核波功能的“漏斗”，它们可以将过多的电子能量迅速转换为核运动。此外，配置项还为电子和核波功能引入了非平凡的几何相位（GPs）。如果人们考虑到CI周围系统的演化，这些阶段就会以波动函数符号的变化来体现。这种符号变化与环绕轮廓的形状无关，因此具有拓扑特征。这些额外的阶段如何影响非绝热动力学是此帐户中要解决的主要问题。