The coherent-state transformation in quantum electrodynamics coupled cluster theory.

Area of Science:

• Quantum Chemistry
• Theoretical Chemistry
• Quantum Electrodynamics

Background:

• Coupled cluster theory is a powerful method for electronic structure calculations.
• Quantum electrodynamics coupled cluster (QED-CC) extends this to include electromagnetic field interactions.
• Coherent-state (CS) transformations offer a novel approach to parameterizing quantum systems.

Purpose of the Study:

• To analyze the coherent-state (CS) transformation within quantum electrodynamics coupled cluster (QED-CC) theory.
• To investigate the impact of CS transformation on the QED-CC Lagrangian and ground state.
• To explore the use of photon-added coherent states as an alternative to displaced number states.

Main Methods:

• Applying a CS transformation to the QED-CC reference state.
• Deriving a QED-CC Lagrangian using CS representations of operators.
• Comparing the use of photon-added coherent states with displaced number states.

Main Results:

• The CS transformation leads to a renormalized QED-CC correlation energy and ground state.
• Renormalization depends on the molecular dipole moment, breaking origin invariance for charged systems.
• Divergent renormalization energy is observed in the low-frequency limit for molecules with dipole moments.

Conclusions:

• The CS transformation provides a new perspective on QED-CC theory, particularly regarding photon basis definition.
• The findings highlight the importance of molecular properties like dipole moments in QED-CC calculations.
• The study suggests potential implications for understanding light-matter interactions in molecular systems.