Mixed semiclassical initial value representation time-averaging propagator for spectroscopic calculations.

Area of Science:

• Quantum chemistry
• Spectroscopy
• Computational physics

Background:

• Semiclassical methods are crucial for simulating molecular dynamics and spectra.
• Existing methods like Herman-Kluk can be computationally expensive for large systems.

Purpose of the Study:

• To derive a computationally efficient mixed semiclassical initial value representation (IVR) for spectroscopic calculations.
• To reduce the computational cost of semiclassical methods while maintaining accuracy.

Main Methods:

• Developed a mixed semiclassical IVR expression incorporating time-averaging filtering and hierarchical properties.
• Introduced a separable approximation to decrease computational expense.
• Tested the method on harmonic and Morse potentials coupled with harmonic degrees of freedom.

Main Results:

• The new approximation reduces computational cost by approximately an order of magnitude compared to full Herman-Kluk.
• Peak positions from the mixed semiclassical method show excellent agreement with exact quantum calculations.
• Overtone peak intensities are slightly lower than exact quantum results.

Conclusions:

• The derived mixed semiclassical method offers a significant reduction in computational cost.
• This approach enables spectroscopic calculations for higher-dimensional systems previously inaccessible.
• The method provides a balance between accuracy and computational efficiency for molecular simulations.