A black-box, general purpose quadratic self-consistent field code with and without Cholesky Decomposition of the two-electron integrals

TL;DR

This paper introduces a robust, black-box quadratic SCF algorithm applicable to various Hartree-Fock methods, capable of exploiting Cholesky decomposition for larger systems and ensuring high convergence without parameter tuning.

Contribution

The implementation of a general-purpose, quadratically convergent SCF algorithm that is black-box, adaptable to different Hartree-Fock references, and utilizes Cholesky decomposition for efficiency.

Findings

The QCSCF algorithm achieves high convergence without parameter tuning.

Cholesky decomposition enables calculations on larger molecular systems.

The method effectively handles difficult convergence cases in high-accuracy computations.

Abstract

We present the implementation of a quadratically convergent Self-consistent field (QCSCF) algorithm based on an adaptive trust-radius optimization scheme for restricted open-shell Hartree-Fock (ROHF), restricted Hartree-Fock (RHF), and unrestricted Hartree-Fock (UHF) references. The algorithm can exploit Cholesky decomposition (CD) of the two-electron integrals to allow calculations on larger systems. The most important feature of the QCSCF code lies in its black-box nature -- probably the most important quality desired by a generic user. As shown for pilot applications, it does not require one to tune the self-consistent field (SCF) parameters (damping, Pulay's DIIS, and other similar techniques) in difficult-to-converge molecules. Also, it can be used to obtain a very thigh convergence with extended basis set - a situation often needed when computing high-order molecular properties - where the standard SCF algorithm starts to oscillate. Nevertheless, trouble may appear even with a QCSCF solver. In this respect, we discuss what can go wrong, focusing on the multiple UHF solutions of ortho-benzyne