Incremental vibrational configuration interaction theory, iVCI: Implementation and benchmark calculations.

Area of Science:

• Quantum Chemistry
• Computational Physics
• Molecular Spectroscopy

Background:

• Configuration Interaction (CI) theory is a cornerstone of quantum chemistry for describing electron correlation.
• Calculating vibrational state energies accurately is crucial for understanding molecular properties and reactivity.
• Traditional methods can be computationally expensive, limiting their application to larger systems.

Purpose of the Study:

• To implement and present a novel algorithm for determining vibrational state energies.
• To leverage a many-body expansion (MBE) approach within the Configuration Interaction (CI) framework.
• To develop an efficient and scalable method for vibrational energy calculations.

Main Methods:

• The study implements an algorithm based on a many-body expansion (MBE) for vibrational state energies.
• An iterative configuration selection scheme is employed for efficient evaluation of MBE increments.
• A threshold function is utilized to reduce the number of increments in higher-order expansions.

Main Results:

• The algorithm demonstrates low memory demands and an embarrassingly parallel workload.
• Convergence of the many-body expansion was studied for formaldehyde, ketene, ethylene, and diborane.
• Benchmark calculations show good agreement with established configuration-selective CI methods.

Conclusions:

• The presented algorithm offers an efficient and computationally feasible approach for calculating vibrational state energies.
• The method's scalability and low memory requirements make it suitable for larger molecular systems.
• This work provides a valuable tool for theoretical investigations in molecular spectroscopy and quantum chemistry.