On the Limited Precision of Transfer of Molecular Optical Activity Tensors

Transfer of molecular property tensors (force field, dipole derivatives, polarizabilities, etc.) from smaller fragments to bigger molecules is powerful tool to calculate molecular vibrational spectra. However, we found serious accuracy limits for valinomycin (Phys. Chem. Chem. Phys. 2010, 12, 11021), where the transfer of the Raman optical activity tensors (ROA) had to be avoided. Therefore, in this study, the individual polarizable group model is analyzed for a model water dimer, and the corrections stemming from mutual group polarizations neglected in the transfer are estimated ab initio. The electric dipole polarizability was found more local and less sensitive to the interaction of distant molecular parts than the optical activity tensors (G′, A), which can partially explain the error observed during the transfer. In the second part of the study, tensor derivatives are transferred from smaller fragments to model valinomycin and insulin molecules, and the resultant tensor derivatives and ROA spectra compared to benchmark computations. The results confirmed that the error is caused by mutual polarization of molecular parts, more significant in insulin than in valinomycin, and could only partially be improved by increased size of the fragments.