Selected configuration interaction method using sampled first-order corrections to wave functions

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Accurate potential energy surfaces are crucial for understanding molecular behavior.
• Calculating these surfaces for quasi-degenerate and excited states presents significant computational challenges.

Purpose of the Study:

• To introduce a new selected configuration interaction (CI) method for computing potential energy surfaces.
• To address the computational demands of quasi-degenerate and excited electronic states.

Main Methods:

• A novel selected configuration interaction (CI) approach was developed.
• Slater determinants were generated using quantum Monte Carlo sampling.
• The wave function was iteratively improved with determinant generation and pruning.

Main Results:

• The new method significantly reduced the number of iterations for convergence compared to standard Monte Carlo CI (MCCI).
• Calculations for the ground and excited states of C2 demonstrated small non-parallelity errors.
• The method proved applicable to potential energy surface calculations.

Conclusions:

• The proposed selected CI method offers an efficient and accurate approach for potential energy surface calculations.
• It is particularly well-suited for quasi-degenerate and excited electronic states.
• The findings suggest broad applicability in theoretical and computational chemistry.