QM/MM Simulations of Vibrational Spectra in Bacteriorhodopsin and Channelrhodopsin-2 Supporting Information

Here, we document the performance of different DFT and DFTB methods with respect to the C−O stretch vibration, both in terms of absolute frequencies and effects of hydrogen bonds on the frequencies. We demonstrate, that PBE/def2-TZVP is a suitable reference for the C−O stretch frequency in carboxylic acids. In the following text, the abbreviations ME (mean error), MAE (mean absolute error), MSE (mean squared error) and GGA (generalized gradient approximation) are used.