How many electrons are excited in an electronic transition? In this Letter, we introduce the excitation number η to answer this question when the initial and final states are each modeled by a single-determinant wave function. We show that calculated η values lie close to positive integers, leading to unambiguous assignments of the number of excited electrons. This contrasts with previous definitions of excitation quantities which can lead to mis-assignments. We consider several examples where η provides improved excited-state characterizations.

中文翻译：

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激发数：表征多重激发态

电子跃迁中有多少电子被激发？在这封信中，当初始状态和最终状态分别由单行波函数建模时，我们引入激励数η来回答这个问题。我们表明，计算出的η值接近正整数，从而导致激发电子数量的明确分配。这与以前的激励量定义相反，后者可能导致分配错误。我们考虑η提供改善的激发态特性的几个例子。