Electrostatically Embedded Many-Body Expansion for Large Systems, with Applications to Water Clusters

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Modeling

Background:

• Incorporating environmental effects on molecular systems is crucial in quantum chemistry.
• Traditional methods often struggle with accuracy and computational cost for large molecular clusters.
• Background molecular charge is a common technique to represent environmental influences.

Purpose of the Study:

• To develop and present electrostatically embedded two-body and three-body expansions for molecular cluster energy calculations.
• To evaluate the accuracy and efficiency of these new methods compared to existing approximations.
• To demonstrate the utility of incorporating environmental electrostatic potentials in fragment-based calculations.

Main Methods:

• The study employs many-body expansions combined with electrostatic embedding.
• Molecular systems are fragmented, and interactions are calculated within the electrostatic field of other fragments.
• Electrostatically embedded pairwise additive (EE-PA) and three-body (EE-3B) expansions were developed and tested.

Main Results:

• The electrostatically embedded methods significantly reduce errors, by up to a factor of 10 for water clusters compared to traditional pairwise additive approximations.
• The EE-3B method achieved an average mean unsigned error of only 0.05 kcal/mol (0.4% of net interaction energy) for various cluster sizes.
• For a 21-molecule water cluster, EE-PA and EE-3B methods showed low errors (2.97 and 0.38 kcal/mol, respectively) relative to full MP2/aug'-cc-pVTZ calculations.

Conclusions:

• Electrostatically embedded many-body expansions provide a highly accurate and efficient approach for calculating molecular cluster energies.
• The method avoids iterative charge determination, offering computational savings for large systems.
• The approach is adaptable to various electronic structure methods and exhibits favorable computational scaling (N(2)/N(3), reducible to O(N)).