Stochastic perturbation theory in a limited configuration space

Area of Science:

• Quantum Chemistry
• Computational Physics
• Theoretical Chemistry

Background:

• Stochastic perturbation theory is derived from configuration interaction wave functions.
• Truncating configuration space in perturbation theory can lead to size-consistency errors.
• Size-consistency is crucial for accurate quantum mechanical calculations.

Purpose of the Study:

• To develop a size-consistent stochastic perturbation theory.
• To address the limitations of truncated configuration interaction methods.
• To provide a robust computational tool for electronic structure calculations.

Main Methods:

• Formulation of a linked variant of stochastic perturbation theory.
• Utilizing the coupled-cluster ansatz as a theoretical framework.
• Implementation based on linearized coupled-cluster theory.

Main Results:

• The linked stochastic perturbation theory preserves size-consistency.
• Results from the linearized coupled-cluster implementation show good agreement with full configuration interaction.
• Comparison with deterministic coupled-cluster and many-body perturbation theories validates the approach.

Conclusions:

• The developed linked stochastic perturbation theory is a viable and accurate method for electronic structure calculations.
• This approach overcomes the size-consistency problem inherent in truncated stochastic methods.
• It offers a promising alternative for complex quantum systems.