Multistate Iterative Qubit Coupled Cluster (MS-iQCC): A Quantum-Inspired, State-Averaged Approach to Ground- And...

Area of Science:

• Quantum chemistry
• Computational physics

Background:

• Accurate prediction of molecular electronic states is vital for spectroscopy and chemical reactivity.
• Existing methods struggle with computational cost for large systems or strong electron correlation.
• Calculating excited states often introduces energetic bias and orthogonality constraints.

Purpose of the Study:

• To introduce a novel quantum-inspired algorithm, MS-iQCC, for efficient computation of molecular ground and excited states.
• To overcome limitations of existing methods in handling strong electron correlation and computational expense.
• To provide a reliable approach for predicting excited-state energetics.

Main Methods:

• Developed the multistate iterative qubit coupled cluster (MS-iQCC) method.
• Employed a state-averaged procedure for simultaneous optimization of multiple electronic states.
• Supported multireference electronic structure with multideterminantal initial guesses and adaptive ansatz construction.

Main Results:

• MS-iQCC demonstrates robust convergence for targeted state energies.
• The method achieves chemically meaningful accuracy across potential energy surfaces.
• Successfully applied to various molecular systems including H4, H2O, N2, and C2, even in strongly correlated configurations.

Conclusions:

• MS-iQCC offers an efficient and accurate approach for calculating ground and excited electronic states.
• The state-averaged procedure eliminates energetic bias in excited-state calculations.
• This method holds promise for advancing computational chemistry, particularly for strongly correlated systems.