Composite Gradient Schemes for Accurate Molecular Geometries: A Flexible Interface and Hierarchical Optimization...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Modeling

Background:

• Accurate molecular geometries are essential for predicting molecular properties and interpreting experimental spectra.
• Composite post-Hartree-Fock methods provide accurate energies but are limited for medium-sized molecules.
• Existing methods lack automated, flexible frameworks for geometry optimization.

Purpose of the Study:

• To develop a flexible, fully automated framework for geometry optimization.
• To integrate density functional theory (DFT) and post-Hartree-Fock methods for enhanced accuracy.
• To enable hierarchical refinement strategies for structural determination.

Main Methods:

• Building upon Pisa Composite Schemes and composite-gradient techniques.
• Integrating Gaussian's internal-coordinate optimizer and analytical derivatives with Molpro's post-Hartree-Fock models.
• Implementing a multilayer PCS2/DFT strategy for larger systems.
• Supporting hierarchical refinement from DFT to composite methods.

Main Results:

• The proposed framework enables automated geometry optimization.
• The workflow successfully integrates DFT and high-accuracy post-Hartree-Fock methods.
• A multilayer strategy extends applicability to larger molecular systems.
• Validation shows consistent, accurate structural determination across diverse molecular systems.

Conclusions:

• The developed automated framework provides accurate molecular geometries.
• This methodology overcomes previous limitations in applying composite methods to medium-sized molecules.
• The flexible workflow enhances the prediction of molecular properties and spectral interpretation.