Understanding the properties of electronically excited states is a challenging task that becomes increasingly important for numerous applications in chemistry, molecular physics, molecular biology, and materials science. A substantial impact is exerted by the fascinating progress in time-resolved spectroscopy, which leads to a strongly growing demand for theoretical methods to describe the characteristic features of excited states accurately. Whereas for electronic ground state problems of stable molecules the quantum chemical methodology is now so well developed that informed nonexperts can use it efficiently, the situation is entirely different concerning the investigation of excited states. This review is devoted to a specific class of approaches, usually denoted as multireference (MR) methods, the generality of which is needed for solving many spectroscopic or photodynamical problems. However, the understanding and proper application of these MR methods is often found to be difficult due to their complexity and their computational cost. The purpose of this review is to provide an overview of the most important facts about the different theoretical approaches available and to present by means of a collection of characteristic examples useful information, which can guide the reader in performing their own applications.

中文翻译：

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分子激发态的多参考方法

理解电子激发态的性质是一项具有挑战性的任务，对于化学，分子物理学，分子生物学和材料科学中的众多应用而言，这变得越来越重要。时间分辨光谱学的引人入胜的进展产生了重大影响，这导致对准确描述激发态特征的理论方法的需求日益增长。对于稳定分子的电子基态问题，现在量子化学方法学发展得如此之快，以至于非专业人士可以有效地使用它，而有关激发态研究的情况则完全不同。这篇评论专门针对一类特定的方法，通常称为多参考（MR）方法，它的通用性是解决许多光谱或光动力问题所必需的。但是，由于它们的复杂性和计算成本，通常很难理解和正确应用这些MR方法。这篇综述的目的是提供有关可用的不同理论方法的最重要事实的概述，并通过收集一些有用的特征示例来介绍有用的信息，这些信息可以指导读者执行自己的应用程序。