Graph-Theory-Based Molecular Fragmentation for Efficient and Accurate Potential Surface Calculations in Multiple...

Area of Science:

• Computational Chemistry
• Theoretical Chemistry
• Quantum Chemistry

Background:

• Calculating multidimensional potential energy surfaces (PES) is crucial for understanding molecular behavior.
• High-level electronic structure methods (e.g., post-Hartree-Fock) provide accuracy but are computationally expensive.
• Density Functional Theory (DFT) offers a cost-effective alternative but may lack accuracy for certain properties.

Purpose of the Study:

• To develop a computationally efficient method for calculating multidimensional PES.
• To achieve accuracy comparable to post-Hartree-Fock methods at the cost of DFT.
• To enable accurate modeling of complex molecular systems, including those with reactive events.

Main Methods:

• A multitopology molecular fragmentation approach based on graph theory.
• Coarse-graining molecular assemblies into graph-theoretic nodes and edges representing subsystems.
• Employing a two-level electronic structure treatment for subsystems within an ONIOM scheme.
• Utilizing many-body expansions and a variational scheme with graph-theoretic representations.
• Implementing a multidimensional clustering algorithm to reduce energy calculations.

Main Results:

• The graph-theoretic approach accurately calculates PES, matching post-Hartree-Fock results.
• The method achieves this accuracy at the computational cost of DFT.
• Rapid convergence of many-body expansions significantly reduces computational scaling.
• Demonstrated accuracy for coupled proton motion in protonated water wires.
• Multidimensional nuclear eigenstates obtained show excellent agreement with high-level calculations.

Conclusions:

• The presented multitopology fragmentation method provides a rigorous and efficient alternative for computing multidimensional PES.
• This approach overcomes the prohibitive computational cost associated with traditional high-level methods for complex systems.
• The method has significant implications for advancing chemical physics research, particularly in areas involving quantum nuclear effects.