Generalized CC-TDSCF and LCSA: The system-energy representation.

Area of Science:

• Quantum mechanics
• Computational chemistry
• Theoretical physics

Background:

• Quantum dynamical problems involving subsystems and baths are typically studied using reduced equations of motion.
• Wavepacket approaches offer a promising avenue for accurately describing subsystem evolution through approximations to the wavefunction.

Purpose of the Study:

• To investigate the performance of continuous-configuration time-dependent self-consistent field (CC-TDSCF) and local coherent-state approximation (LCSA) methods.
• To enhance these methods by replacing discrete variable representation (DVR) states with energy-localized eigenstates of the subsystem Hamiltonian.

Main Methods:

• The study focuses on CC-TDSCF and LCSA methods.
• It replaces the standard DVR states with energy-local representations derived from subsystem Hamiltonian eigenstates.
• The modified methods are applied to various dissipative quantum dynamical problems.

Main Results:

• Stable and semiquantitative results were achieved for dissipative problems.
• The computational cost remained low, comparable to the original CC-TDSCF and LCSA methods.
• Both modified methods produced highly similar results, indicating the suitability of coherent-states for describing bath states.

Conclusions:

• The choice of the system basis-set is crucial for accurate wavefunction expansion in selected-multiconfiguration methods.
• Optimizing subsystem states variationally within CC-TDSCF/LCSA offers a pathway to computationally inexpensive yet accurate quantum dynamics simulations.