Anharmonic vibrational eigenfunctions and infrared spectra from semiclassical molecular dynamics

Area of Science:

• * Computational Chemistry
• * Molecular Spectroscopy
• * Quantum Dynamics

Background:

• * Accurate simulation of molecular infrared (IR) spectra is crucial for understanding chemical processes.
• * Traditional methods often struggle to incorporate anharmonic effects and scale poorly with system dimensionality.
• * Existing quantum mechanical benchmarks can be computationally expensive.

Purpose of the Study:

• * To develop a new semiclassical molecular dynamics approach for simulating IR absorption and emission spectra.
• * To incorporate anharmonic intensities into spectral simulations.
• * To provide an intuitive assignment of spectral peaks.

Main Methods:

• * Utilizes semiclassical molecular dynamics to compute power spectra.
• * Calculates vibrational eigenfunctions as linear combinations of harmonic states.
• * Determines oscillator strengths for vibrational transitions, avoiding grid calculations.

Main Results:

• * The method successfully simulates IR spectra with anharmonic intensities.
• * Validation against a 1D Morse potential and water molecule shows excellent agreement with quantum benchmarks.
• * Demonstrates scalability to high-dimensional systems by avoiding exponential basis set scaling via truncation.

Conclusions:

• * The proposed semiclassical approach provides accurate IR spectra beyond the harmonic approximation.
• * It offers an intuitive assignment of spectral peaks related to normal modes.
• * The method is computationally efficient and scalable for complex molecular systems.