VSCF/VCI theory based on the Podolsky Hamiltonian

Area of Science:

• Computational Chemistry
• Molecular Spectroscopy
• Quantum Mechanics

Background:

• Calculating vibrational spectra of semi-rigid molecules often uses the Watson Hamiltonian.
• Floppy molecules and clusters require Hamiltonians that handle curvilinear coordinates, but their kinetic energy operators (KEO) are computationally expensive.
• Existing methods face challenges with computational cost for complex molecular systems.

Purpose of the Study:

• To implement novel vibrational self-consistent field (VSCF) and vibrational configuration interaction (VCI) theories.
• To utilize the Podolsky Hamiltonian with an n-mode expansion for the inverse metric tensor (G matrix).
• To analyze the computational cost and accuracy of the new method for molecular vibrational spectra.

Main Methods:

• Developed a new implementation of VSCF and VCI theories using the Podolsky Hamiltonian.
• Represented the inverse metric tensor (G matrix) using a polynomial-based n-mode expansion.
• Analyzed the contribution of individual KEO terms based on n-mode expansion truncation orders.

Main Results:

• The novel implementation provides accurate vibrational spectra for challenging molecules.
• Benchmark calculations for cis-HOPO and methanimine (H2CNH) show good agreement with experimental data.
• The study analyzes the importance of KEO terms concerning n-mode expansion truncation.

Conclusions:

• The new method offers a more computationally tractable approach for calculating vibrational spectra of floppy molecules.
• The n-mode expansion of the G matrix is effective in managing computational costs.
• This work advances the accuracy and efficiency of theoretical vibrational spectroscopy.