On-The-Fly Dynamics of Multiconfigurational Wave Packets by a Semiclassical Method

Area of Science:

• Quantum chemistry
• Theoretical chemistry
• Chemical dynamics

Background:

• Accurate simulation of nuclear dynamics is crucial for understanding chemical reactions and spectroscopy.
• Existing methods like multiconfiguration time-dependent Hartree (MCTDH) often require computationally expensive prefitted potential energy surfaces.
• There is a need for efficient methods that can handle multimode couplings and electronic transitions.

Purpose of the Study:

• To introduce a novel on-the-fly, trajectory-based semiclassical scheme for time propagation of multiconfigurational nuclear wave packets (MCWPs).
• To enable MCWP time propagation without relying on a prefitted global potential energy surface.
• To extend the method to study transitions between electronic states.

Main Methods:

• Development of an on-the-fly semiclassical scheme for MCWP time propagation.
• Comparison with the matrix-product-state MCTDH method for formaldehyde dynamics.
• Calculation of on-the-fly infrared spectra for benzene and simulation of benzene fluorescence incorporating Herzberg-Teller coupling.

Main Results:

• The proposed semiclassical method achieves accurate wave packet propagation, validated by comparisons with the matrix-product-state MCTDH method.
• On-the-fly infrared spectra of benzene calculated using this method show excellent agreement with experimental data.
• The scheme successfully reproduces the characteristic vibronic structure in benzene fluorescence, including Herzberg-Teller coupling effects.

Conclusions:

• The on-the-fly semiclassical approach provides an accurate and efficient alternative for nuclear wave packet propagation.
• This method overcomes the limitation of requiring prefitted potential energy surfaces, offering computational advantages.
• The scheme's applicability to electronic transitions and its ability to reproduce experimental spectroscopic features highlight its potential for complex chemical systems.