Geometry optimization for large systems by the elongation method

Abstract

Geometry optimization using the elongation method is developed at the Hartree–Fock level of theory. The formalism of elongation energy gradient and its accuracy have been validated by model systems calculations. The linear poly-hydrogen fluoride, polyethylene, planar polyacetylene and extended polyalanine are optimized using different basis sets and compared with conventional results. The results show that the elongation Hartree–Fock geometry optimization (ELG-HF-OPT) can reproduce conventional calculation results with high accuracy for various basis sets. For the poly-hydrogen fluoride calculation at 6-31G(d,p) basis set, moreover, ELG-HF-OPT gives a structure with lower ground state energy than conventional results with the same optimization convergence threshold. This means the potential possibility of ELG-HF-OPT can locate a more stable structure than conventional calculations with the same optimization convergence criteria. Therefore, the ELG-HF-OPT would provide one more choice for performing optimization on complicated large systems.