Calculation of Dipole Transition Matrix Elements and Expectation Values by Vibrational Coupled Cluster Method

Area of Science:

• Quantum Chemistry
• Computational Spectroscopy
• Molecular Physics

Background:

• Coupled cluster (CC) methods are powerful tools for electronic structure calculations.
• Accurate calculation of vibrational properties and transition matrix elements is crucial for spectroscopy.
• Linear response theory is essential for studying excited states.

Purpose of the Study:

• To develop and apply an effective operator approach using coupled cluster methods.
• To investigate the convergence of vibrational properties and transition matrix elements.
• To compare the performance of extended coupled cluster (ECCM) with normal coupled cluster (NCCM).

Main Methods:

• Coupled cluster linear response theory (CCLRT) for excited states.
• Effective operator approach based on coupled cluster.
• Arponen-type double similarity transformation within ECCM framework.

Main Results:

• The coupled cluster method accurately describes low-lying vibrational excited states.
• Convergence patterns of properties were studied with respect to excitation operator rank.
• ECCM demonstrated significant improvement in calculating transition matrix elements.

Conclusions:

• The coupled cluster method is reliable for vibrational excited state calculations.
• ECCM offers enhanced accuracy for transition matrix elements.
• This approach provides a robust framework for molecular property calculations.