Quadratically convergent self-consistent field of projected Hartree-Fock

Area of Science:

• Quantum Chemistry
• Computational Physics

Background:

• Spin-projected unrestricted Hartree-Fock (SUHF) methods are crucial for describing systems with spin contamination.
• Traditional SUHF algorithms can suffer from slow convergence, particularly when dealing with small eigenvalues in the orbital Hessian matrix.

Purpose of the Study:

• To develop a robust and efficient algorithm for solving SUHF equations.
• To accelerate the convergence of SUHF calculations through a quadratically convergent approach.

Main Methods:

• Implementation of a quadratically convergent self-consistent field (QC-SCF) algorithm tailored for SUHF.
• Testing the QC-SCF algorithm on systems exhibiting significant non-dynamic correlation.

Main Results:

• The developed QC-SCF algorithm demonstrates robustness and stability.
• The new method significantly accelerates the convergence of SUHF calculations compared to traditional approaches.
• Performance is validated against established methods like Roothaan repeated diagonalization, Pople extrapolation, and direct inversion of iterative subspace.

Conclusions:

• The QC-SCF algorithm provides a highly efficient and stable route to obtain SUHF solutions.
• This advancement is particularly beneficial for quantum chemistry problems with substantial non-dynamic correlation.
• The method offers a practical improvement for computational studies requiring accurate spin-projected wavefunctions.