Raman spectral calculation by vibrational coupled-cluster method in bosonic representation

Abstract

ABSTRACTWe present a method to calculate the Raman spectra of poly-atomic molecules using the vibrational coupled-cluster method in bosonic representation. The effective operator-based approach with Arponen's extended coupled-cluster ansatz is used to calculate the transition matrix elements associated with the polarisability surface to calculate the Raman intensities. A test calculation is made on furan and the resultant spectrum is compared with the experimental spectrum. The agreement between the theoretical anharmonic spectrum and experimental spectrum is quite good. An observation made from these calculations is that the transitions in the 3000–3200 cm−1 range (CH stretch) is dominated by several transitions to final states that are dominated by multiple quantum states and hardly to any single fundamental state. We used both dynamic and static polarisabilities and found that the spectra generated from these two polarisability tensors are practically identical, implying that the polarisability tensor is insensitive to the incident frequency.