Advanced concepts in vibrational configuration interaction theory (VCI)

近年来，分子和分子团簇的非简谐振动频率的变分计算引起了人们的极大兴趣。然而，所采用的方法面临着两个计算瓶颈，即用复杂的电子结构方法精确计算多维势能面和考虑振动关联效应。该方案侧重于后一方面，并提出了新的想法，旨在降低计算成本和存储需求，以及平衡处理具有准简并振动态的分子。本质上，应开发一种新的组态选择多态振动组态相互作用程序，该程序允许对比现有程序更大的系统进行平衡计算，并且不限于关联空间和势能面的任何展开式。一旦新程序投入使用，它将应用于振动光谱学中的最新问题，以及对金属卤化物(MX)_n团簇的研究，这些团簇的原子最多可达20个。

The variational calculation of anharmonic vibrational frequencies of molecules and molecular clusters has gained considerable interest in the recent past. However, the methods employed face two computational bottlenecks, i.e. the accurate calculation of a multidimensional potential energy surface by sophisticated electronic structure methods and the account of vibration correlation effects. This proposal focuses on the latter aspect and new ideas are presented, which aim at the reduction of the computational cost and memory requirements as well as a balanced treatment of molecules with quasi-degenerate vibrational states. Essentially, a new configuration selective multistate vibrational configuration interaction program shall be developed, which allows for the balanced calculation of larger systems than the present code and which is not limited in any expansion orders of the correlation space and the representation of the potential energy surface. Once the new program is operative, it shall be applied to state-of-the-art problems in vibrational spectroscopy and the investigation of metal halide, (MX)_n, clusters with up to 20 atoms.