Mixed-quantum-classical or fully-quantized dynamics? A unified code to compare methods.

Area of Science:

• Quantum Chemistry
• Theoretical Chemistry
• Chemical Dynamics

Background:

• Accurate simulation of chemical reactions requires methods that go beyond the Born-Oppenheimer approximation.
• Non-adiabatic dynamics methods are crucial for understanding processes where electronic and nuclear motions are coupled.

Purpose of the Study:

• To compare the capabilities of three distinct non-adiabatic dynamics methods.
• To introduce a novel approach for comparing quantum dynamics simulations.

Main Methods:

• Comparison of Multi-configurational time-dependent Hartree (MCTDH), variational Multi-configurational Gaussian (vMCG), and trajectory surface hopping (TSH).
• Direct dynamics calculations using vMCG and TSH with on-the-fly quantum chemistry.
• Development of a time-dependent discrete variable representation (TD-DVR) for calculating adiabatic populations from grid-based dynamics.

Main Results:

• All three methods were applied to a model Hamiltonian.
• vMCG and TSH demonstrated direct dynamics capabilities.
• The novel TD-DVR approach enables accurate comparison of adiabatic populations across different dynamics methods.

Conclusions:

• The study provides a framework for evaluating and comparing different non-adiabatic dynamics techniques.
• The developed TD-DVR method enhances the comparability of quantum dynamics simulations.
• This work contributes to the accurate modeling of chemical processes without the Born-Oppenheimer approximation.