Robust ΔSCF calculations with direct energy functional minimization methods and STEP for molecules and materials

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Accurate calculation of electronic excitation energies is crucial for understanding molecular properties and chemical reactions.
• Traditional Δ self-consistent field (ΔSCF) methods can face convergence challenges, particularly for complex systems.
• The CP2K program package offers a platform for advanced quantum chemical simulations.

Purpose of the Study:

• To implement and evaluate the orbital transformation (OT) scheme within the CP2K package for Δ self-consistent field (ΔSCF) calculations.
• To assess the applicability and robustness of the OT-based ΔSCF method for various molecular and periodic systems.
• To investigate vertical excitation energies of specific heteroaromatic molecules, condensed-phase systems, and surface-adsorbed molecules.

Main Methods:

• Direct energy functional minimization using the orbital transformation (OT) scheme.
• Application of the Δ self-consistent field (ΔSCF) method for calculating vertical excitation energies.
• Implementation of a state-targeted energy projection ΔSCF algorithm for diagonalization-based SCF in CP2K.
• Investigation of molecules and periodic systems, including solvated species and surface-adsorbed complexes.

Main Results:

• The OT scheme demonstrated smooth and robust self-consistent field (SCF) convergence for all investigated excitation energies.
• The ΔSCF method, enhanced by OT, was successfully applied to diverse systems, including heteroaromatic molecules, solvated ethylene, solvated uracil, and a Re-phosphate/TiO2 system.
• The implemented state-targeted energy projection algorithm further supports ΔSCF calculations within CP2K.

Conclusions:

• The orbital transformation (OT) scheme provides a reliable and efficient approach for ΔSCF calculations, overcoming convergence issues.
• The developed methodology is versatile, applicable to both molecular and periodic systems for accurate excitation energy determination.
• This work advances computational tools for studying electronic properties of complex chemical and material systems.