An Accurate Quantum-Based Approach to Explicit Solvent Effects: Interfacing the General Effective Fragment Potential...

Area of Science:

• Computational Chemistry
• Quantum Mechanics
• Intermolecular Interactions

Background:

• Accurate modeling of intermolecular interactions is crucial in chemistry and biology.
• Existing methods like Effective Fragment Potential (EFP2) have limitations in accuracy for certain components.
• Combining ab initio quantum mechanics (QM) with EFP2 offers a potential for improved accuracy.

Purpose of the Study:

• To implement and validate a QM-EFP2 interface for accurate calculation of intermolecular interactions.
• To improve the accuracy of exchange repulsion and dispersion components in QM-EFP2 calculations.
• To assess the performance of the new QM-EFP2 method for molecular systems, including water clusters.

Main Methods:

• Developed a QM-EFP2 interface incorporating Coulomb, polarization, exchange repulsion (exrep), and dispersion.
• Replaced the EFP2-EFP2 spherical Gaussian overlap approximation with exact electron repulsion integrals (ERI) for exrep.
• Implemented Gaussian damping for Coulomb and overlap damping for dispersion components.
• Utilized symmetry-adapted perturbation theory (SAPT) and coupled cluster theory [CCSD(T)] for benchmarking.
• Employed distributed data interface (DDI) parallelization for computational efficiency.

Main Results:

• The QM-EFP2 method demonstrates excellent agreement with SAPT for component energies and CCSD(T) for total interaction energies.
• Benchmarking against S22 and S66 data sets shows high accuracy.
• Calculations on water clusters up to 256 molecules confirm accuracy comparable to EFP2-EFP2 and MP2.
• The QM-EFP2 Fock operator formation scales linearly with EFP basis functions for water clusters.

Conclusions:

• The implemented QM-EFP2 method provides an accurate and efficient approach for studying intermolecular interactions.
• The use of exact ERIs and novel damping functions significantly enhances the reliability of the exrep and dispersion calculations.
• QM-EFP2 offers a computationally viable alternative to traditional methods for large molecular systems.