Geminal model chemistry. IV. Variational and size consistent pure spin states

Area of Science:

• Quantum chemistry
• Computational physics
• Electronic structure theory

Background:

• Accurate calculation of ground state wave functions is crucial in quantum chemistry.
• Existing methods often face challenges with computational cost, size consistency, or adjustable parameters.
• Spin symmetry is a key property for understanding molecular electronic states.

Purpose of the Study:

• To introduce a computationally inexpensive method for obtaining ground state wave functions.
• To ensure the method is variational, size consistent, and free from adjustable parameters.
• To demonstrate the method's applicability to various chemical systems.

Main Methods:

• The method employs partially spin restricted geminal wave functions.
• It incorporates limited spin contamination to maintain computational efficiency.
• The approach is variational and rigorously size consistent.

Main Results:

• The method achieves pure spin symmetry for ground state wave functions.
• It exhibits favorable scaling with system size, making it efficient for larger systems.
• Computations on bond breaking, transition metal compounds, and hydrogen clusters validated the method's properties.

Conclusions:

• The presented method offers a computationally inexpensive and accurate way to compute ground state wave functions.
• Its rigorous size consistency and lack of adjustable parameters enhance its reliability.
• The method shows promise for diverse applications in quantum chemistry and materials science.