Photon absorption (OPA) and electronic circular dichroism (ECD) spectra of the conformers of bco_tyr

In a following step we run new unconstrained optimizations from the constrained minima, in order to check if new true minima are found or alternatively the optimization found again the minima discussed in the first part of this report. New stationary points for both cis and trans are actually obtained. However, there are no improvements for the distance d. While for the trans a new minimum with d=2.6 Ang, more stable than the original one is found the optimization of cis essentially finds the same structure already discussed above.

In this report we investigate the one photon absorption (OPA) and electronic circular dichroism (ECD) spectra of the conformers of bco_tyr sketched in Figure 1. Ground state equilibrium geometries were obtained at DFT level checking that frequencies were all positive. We adopted both B3LYP and CAM-B3LYP functionals in gas phase, using the Gaussian 09 program. In order to improve the description of dispersion interactions, we also employed Grimme's GD3 correction. A relaxed Potential Energy Surface scan was performed to study the relationship between the conformers and the distances d highlighted in the experiment. Different basis sets have been used from 6-31g(d,p) to 6-311+G(d,p).