The Perturbed Matrix Method is one of the methods to carry out theoretical studies on infrared spectroscopy at a low computational cost. One of the main assumptions adopted up to now is the invariant mode approximation: the actual mass-weighted Hessian eigenvectors of a vibrational center embedded in a chemical environment can be well approximated by the vacuum Hessian eigenvectors with the environment perturbation affecting only the mode frequencies. Herein, we investigate the accuracy of this approximation considering different scenarios. The results demonstrate the accuracy of this approximation providing non-negligible mode coupling only when dealing with extremely intense perturbation fields.

摄动矩阵法是以较低的计算成本进行红外光谱理论研究的方法之一。到目前为止，采用的主要假设之一是不变模式近似：化学环境中嵌入的振动中心的实际质量加权Hessian特征向量可以通过真空Hessian特征向量很好地近似，其中环境扰动仅影响模式频率。在本文中，我们研究了考虑不同情况的近似方法的准确性。结果表明，仅当处理极强的扰动场时，这种近似的精度才提供不可忽略的模式耦合。