OpenOrbitalOptimizer─A Reusable Open Source Library for Self-Consistent Field Calculations

Area of Science:

• Computational Chemistry
• Software Engineering

Background:

• Modern software engineering emphasizes reusable open-source libraries for complex tasks.
• Solving self-consistent field (SCF) equations is a fundamental challenge in computational chemistry.

Purpose of the Study:

• To introduce OpenOrbitalOptimizer, a novel C++ library for the iterative solution of coupled SCF equations.
• To provide a flexible tool for integrating advanced convergence accelerators into existing quantum chemistry programs.

Main Methods:

• The library implements standard SCF algorithms: Pulay's direct inversion in the iterative subspace (DIIS), energy DIIS (EDIIS), augmented DIIS (ADIIS), and optimal damping algorithm (ODA).
• OpenOrbitalOptimizer requires only functions for total energy and Fock matrix evaluation, and assumes Fock/orbital matrices can be stored in memory and diagonalized.

Main Results:

• The library was exemplified with nuclear-electronic orbital (NEO) calculations of protonated water clusters.
• A minimal-basis protonic guess was found effective.
• The stepwise SCF algorithm demonstrated superior computational efficiency compared to the simultaneous SCF algorithm.

Conclusions:

• OpenOrbitalOptimizer offers an accessible method to incorporate state-of-the-art convergence techniques into quantum chemistry software.
• The library's design facilitates integration with legacy programs, streamlining computational workflows.
• The study highlights the efficiency of the stepwise SCF algorithm for NEO calculations.