Converging many-body correlation energies by means of sequence extrapolation

Area of Science:

• Computational quantum chemistry
• Many-body theory
• Theoretical chemistry

Background:

• Accurate calculation of correlation energy is crucial for predicting molecular properties.
• Traditional methods face significant computational scaling issues with increasing system size.
• The virtual space, essential for correlation, often requires a vast number of orbitals.

Purpose of the Study:

• To introduce an efficient extrapolation scheme for correlation energy.
• To reduce the computational cost associated with large virtual spaces in quantum chemistry.
• To enable accurate ab initio calculations for complex systems.

Main Methods:

• Developed an extrapolation scheme for correlation energy.
• The scheme selectively uses a small fraction of virtual orbitals.
• Applied the method to both single- and multi-reference problems.

Main Results:

• The extrapolation scheme recovers nearly the entire dynamic correlation energy.
• It significantly reduces the number of orbitals required compared to traditional methods.
• Demonstrated effectiveness in ground-state and excited-state (photochemistry) calculations.

Conclusions:

• The proposed scheme effectively overcomes the scaling limitations in ab initio quantum chemistry.
• It provides a computationally feasible route to highly accurate correlation energy calculations.
• Applicable to a wide range of quantum chemistry problems, including complex molecular systems.