Development of efficient vibration correlation methods for floppy molecules

• Applicant: Professor Dr. Guntram Rauhut
• Subject Area: Theoretical Chemistry: Electronic Structure, Dynamics, Simulation
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 559224931

The accurate simulation of molecular infrared spectra requires the inclusion of vibration correlation effects. For semi-rigid molecules this can be realized by approaches relying on the Watson Hamiltonian. However, for floppy molecules with large amplitude motions, which cannot properly be represented by rectilinear coordinates, a more generalized Hamiltonian needs to be employed. This is offered by the Podolsky Hamiltonian, which unfortunately has a rather complicated form. While a new and efficient implementation of time-independent vibrational self-consistent field theory (VSCF) based on the Podolsky Hamiltonian has been provided quite recently, efficient methods accounting for vibration correlation effects are still missing. A hierarchy of methods, ranging from 2nd order (quasi-degenerate) vibrational Moller-Plesset perturbation theory to configuration-selective vibrational configuration interaction theory (VCI), shall be developed, which allow for the simulation of vibrational spectra in arbitrary coordinates. Moreover, the series expansion of the Podolsky Hamiltonian shall be augmented by high-order terms and benchmark calculations for floppy molecules shall be provided, which allow for a direct comparison with experimental data.

• DFG Programme: Research Grants