Partial Atomic Charges and Screened Charge Models of the Electrostatic Potential

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Modeling

Background:

• Accurate calculation of partial atomic charges is crucial for understanding molecular properties and interactions.
• Conventional electrostatic potential (ESP) fitting methods often rely on simplified point-charge models.
• Existing screened charge methods like outer density screening (ODS) offer improvements but can be further refined.

Purpose of the Study:

• To develop and evaluate a novel screened charge method, full density screening (FDS), for calculating partial atomic charges.
• To compare the performance of FDS against conventional point-charge ESP fitting and the ODS method.
• To assess the accuracy and sensitivity of derived atomic charges to fitting point positions.

Main Methods:

• The full density screening (FDS) model approximates atomic screening effects using charge densities distributed in Slater-type orbitals (STOs).
• The outer density screening (ODS) model, previously proposed, represents charge density as a sum of a point charge and a smeared negative charge in an STO.
• Parameters (ζ values of STOs) for both FDS and ODS were optimized to best reproduce electrostatic potentials.

Main Results:

• Screened charge methods, particularly FDS, significantly improve the quality of ESP fitting, especially near atomic centers.
• Atomic charges derived using screened charges exhibit reduced sensitivity to the placement of fitting points compared to conventional methods.
• FDS charges are comparable to point-charge methods, with ODS showing higher accuracy for electronic embedding in QM/MM simulations.

Conclusions:

• The FDS model is recommended for ESP fitting and ESP field reproduction.
• The ODS model is superior for QM/MM applications due to its accuracy in electronic embedding.
• Screened charge methods provide a more realistic and robust representation of electrostatic potentials than traditional point-charge models.