Iterative diagonalization in the multiconfigurational time-dependent Hartree approach: ro-vibrational eigenstates.

Area of Science:

• Quantum Chemistry
• Molecular Spectroscopy
• Computational Physics

Background:

• Calculating ro-vibrational eigenstates is crucial for understanding molecular dynamics.
• Existing methods, like the multiconfigurational time-dependent Hartree (MCTDH) approach, face computational challenges for rotational states (J > 0).

Purpose of the Study:

• To develop an efficient computational scheme for determining ro-vibrational eigenstates (J > 0) within the MCTDH framework.
• To enable accurate calculations of molecular rotational and vibrational energy levels.

Main Methods:

• Introduced a novel scheme utilizing a basis of pre-calculated MCTDH wave packets (from J=0 calculations).
• Combined these wave packets with Wigner rotation matrices to form a ro-vibrational basis for J > 0.
• Employed iterative diagonalization within the MCTDH approach for efficient Hamiltonian matrix computation.

Main Results:

• The proposed method efficiently calculates accurate ro-vibrational states for various J values.
• Test calculations on CH2D demonstrated convergence within wavenumber accuracy for moderately large J.
• The number of iterations increased significantly for very large J or high accuracy requirements.

Conclusions:

• The new MCTDH-based scheme provides an efficient and accurate way to compute ro-vibrational eigenstates.
• The method's accuracy was validated by comparing theoretical results with experimental data for CH2D.
• This approach facilitates the investigation of potential energy surfaces through accurate spectral predictions.