SS(p)G: a strongly orthogonal geminal method with relaxed strong orthogonality

Area of Science:

• Quantum chemistry
• Computational chemistry

Background:

• Strong orthogonality is a constraint in geminal wavefunctions for tractable variational minimization.
• This constraint can exclude important excited configurations from ground state descriptions.

Purpose of the Study:

• To develop a method that removes the strong orthogonality constraint from geminal wavefunctions.
• To introduce a perturbative-like correction for independent geminal improvement.

Main Methods:

• Applied a novel method, Singlet-type Strongly orthogonal Geminals with perturbation (SS(p)G), to lift the strong orthogonality constraint.
• Compared SS(p)G with non-orthogonal AP1roG and Geminal Mean-Field Configuration Interaction (GMFCI).
• Assessed scalability using Density Matrix Renormalization Group (DMRG) on polyene chains.

Main Results:

• The perturbative correction, though small, was found to be significant.
• Demonstrated the method's applicability to small atomic and molecular systems.
• Evaluated the method's potential for large, strongly correlated systems.

Conclusions:

• The developed perturbative correction is a crucial initial step for systematically improving strongly orthogonal geminal methods.
• The SS(p)G method shows promise for describing chemical systems more accurately by addressing limitations of strong orthogonality.