Long-Range Configuration Interaction with an Ab Initio Short-Range Correction and an Asymptotic Lower Bound†

Area of Science:

• Quantum chemistry
• Computational physics
• Many-body theory

Background:

• Accurate calculation of electron correlation is crucial in quantum chemistry.
• Long-range and short-range electron interactions require different treatment methods.
• Configuration interaction (CI) methods are computationally demanding.

Purpose of the Study:

• To develop a rigorous method for short-range corrections to long-range selected configuration interaction (SRcLRCI).
• To apply the method to harmonium models with 2-6 electrons.
• To assess the accuracy and applicability to ground and excited states.

Main Methods:

• Derivation of short-range corrections from perturbation theory.
• Application to harmonium models using a long-range/short-range separation at ~1 atomic unit.
• Calculation of total energies for low-lying states.

Main Results:

• The SRcLRCI method provides energies within chemical accuracy.
• The second-order perturbation expression yields a lower bound to the full CI energy.
• Results for harmonium systems outperform short-range density functional approximations.

Conclusions:

• The developed SRcLRCI method is accurate and applicable to various electronic states.
• This approach offers a computationally viable alternative to traditional methods.
• The findings suggest potential for improved electronic structure calculations.