Analytical energy gradient for reference interaction site model self-consistent field explicitly including spatial...

Area of Science:

• Computational Chemistry
• Theoretical Chemistry
• Physical Chemistry

Background:

• The Reference Interaction Site Model Self-Consistent Field (RISM-SCF) is a powerful method combining ab initio electronic structure theory and statistical mechanics for studying molecular liquids.
• Previous work established RISM-SCF with Explicitly Including Spatial Electron Density Distribution (RISM-SCF-SEDD) as a numerically stable approach, expanding the scope of solvation theory.
• Accurate computation of molecular geometry requires energy gradient calculations, a capability previously lacking in RISM-SCF-SEDD.

Purpose of the Study:

• To derive an analytical energy gradient formula for the RISM-SCF-SEDD method.
• To implement and apply the new energy gradient capability to investigate solvation effects on molecular systems.
• To validate the method's accuracy by comparing results with experimental data.

Main Methods:

• Derivation of the analytical energy gradient formula for RISM-SCF-SEDD.
• Application of the developed method to aqueous solutions, focusing on the hydration structure and geometry of the phosphate anion (PO4^3-).
• Investigation of the tautomerization process between 2-pyridone and 2-hydroxypyridine in aqueous solution.

Main Results:

• The implemented RISM-SCF-SEDD method with energy gradients accurately reproduced the hydration structure and geometry of the phosphate anion.
• The method correctly predicted the relative energies of the tautomers of 2-pyridone and 2-hydroxypyridine in aqueous solution.
• Microscopic solvent distribution was successfully captured, providing detailed insights into solvation effects.

Conclusions:

• The derived analytical energy gradient formula significantly enhances the RISM-SCF-SEDD method's capabilities for molecular geometry optimization in solution.
• The RISM-SCF-SEDD approach, coupled with advanced quantum chemical calculations like coupled cluster, provides a powerful tool for accurate molecular property evaluation.
• This method offers a reliable means to study complex chemical systems in solution, bridging quantum mechanics and statistical mechanics.