Dissecting the Hydrogen Bond: A Quantum Monte Carlo Approach

Area of Science:

• Quantum chemistry
• Computational physics
• Chemical physics

Background:

• The water dimer is a fundamental model system for understanding hydrogen bonding.
• Accurate theoretical descriptions of weakly interacting systems are crucial for chemical insights.

Purpose of the Study:

• To investigate the dissociation energy and dispersion curve of the water dimer using Quantum Monte Carlo (QMC).
• To analyze the contributions of different energy components (dispersive, covalent) to the binding energy.
• To assess the performance of the Jastrow Antisymmetrised Geminal Power (JAGP) wave function and Lattice Regularized Diffusion Monte Carlo (LRDMC) method.

Main Methods:

• Utilized a variational wave function: Jastrow Antisymmetrised Geminal Power (JAGP).
• Employed Lattice Regularized Diffusion Monte Carlo (LRDMC) for improved correlation energy.
• Systematically analyzed energy contributions by selectively disabling variational terms in the JAGP wave function.

Main Results:

• Obtained a binding energy of -4.5(0.1) kcal/mol variationally, improved to -4.9(0.1) kcal/mol with LRDMC, closely matching experimental values.
• Successfully reproduced the minimum position, curvature, and asymptotic behavior of the dispersion curve.
• Quantified the dispersive van der Waals contribution at 1.5(0.2) kcal/mol and the intermolecular covalent energy at 1.1(0.2) kcal/mol.

Conclusions:

• The QMC approach with the JAGP wave function provides a reliable and accurate method for studying weakly interacting systems.
• Both dispersive and covalent interactions are significant contributors to the water dimer's binding energy.
• This methodology offers a promising tool for quantitative descriptions of systems dominated by non-covalent interactions.