# Vibrational Analysis Tools¶

The vibrational analysis tools in AMS provides several specialized methods for the calculation of normal modes and their properties. These are available as the VibrationalAnalysis task in AMS. The applications herein can be split in roughly two categories: mode selective analysis and vibronic couplings. Their input is controlled by the VibrationalAnalysis input block.

There are three mode selective analysis methods in the Vibrational Analysis tools: Mode Scanning, Mode Refinement and Mode Tracking. The latter two methods can be used for the calculation of select modes or select regions of the vibrational IR spectrum, whereas Mode Scanning can be used to obtain more accurate approximations of the vibrational mode properties.

In addition, there are three methods for the calculation of vibronic couplings in absorption spectra: Vibronic-Structure, Vibronic-Structure Tracking and Vibronic-Structure Refinement. The first of these methods is a pure implementation of the Vertical Gradient Franck-Condon (VG-FC) method, also called Independent Mode Displaced Harmonic Oscillator model (IMDHO), for the calculation of vibronic couplings. The latter two methods apply respectively the mode tracking and mode refinement concepts to the calculation of the normal modes needed for the VG-FC model, thereby significantly reducing computation times.

Finally, the VG-FC resonance Raman application applies this same VG-FC model to the calculation of resonance Raman spectra.

All of these methods belong to the VibrationalAnalysis task in the AMS driver. This means that they all share the same input block VibrationalAnalysis for their settings and input options. One can select a specific application using the Type keyword in this input block. Here we will give an overview of the different functionalities within the VibrationalAnalysis task and discuss some of the core input options shared among all tasks. All of these methods are discussed in more detail on their respective pages.