Energy benchmarks for water clusters and ice structures from an embedded many-body expansion

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Accurate calculation of ab initio energies for water clusters and ice is crucial for understanding their properties.
• Traditional methods can be computationally expensive for large systems.

Purpose of the Study:

• To demonstrate the effectiveness of the embedded many-body expansion (EMBE) for calculating accurate ab initio energies of water clusters and ice.
• To assess the accuracy of EMBE when applied to wavefunction-based methods.

Main Methods:

• Utilized the embedded many-body expansion (EMBE) approach, separating energy into Hartree-Fock and correlation components.
• Applied EMBE specifically to the correlation energy, using standard quantum chemistry for clusters and plane-wave methods for crystals.
• Tested EMBE with second-order Møller-Plesset (MP2) and coupled-cluster methods.

Main Results:

• EMBE truncated at the 2-body level accurately reproduced correlation energies for water clusters (up to 16-mer) using MP2, with errors less than 0.1 mE(h)/monomer.
• MP2 energies for ice structures (Ih, II, VIII) near the complete basis-set limit showed good agreement with experimental binding energies.
• Coupled-cluster methods were found essential for describing non-additive dispersion in ice structures.

Conclusions:

• EMBE is a reliable and efficient method for calculating accurate ab initio energies of water clusters and ice.
• The method shows promise for future applications in condensed matter physics and chemistry.
• Combining EMBE with advanced wavefunction methods provides a powerful tool for studying complex molecular systems.