Efficient High-Level Quantum Chemical Exploration of Clathrate Hydrates via Fragmentation

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Clathrates are cage-like structures that can trap gas molecules.
• Accurate computational methods are needed to understand clathrate properties.
• Previous studies may have lacked the accuracy or scale for complex clathrate systems.

Purpose of the Study:

• To perform high-accuracy energetic calculations on clathrates containing CO2, CH4, and H2S.
• To compute and analyze the vibrational infrared (IR) spectra of these clathrates.
• To demonstrate the feasibility of advanced computational methods for large molecular systems.

Main Methods:

• Fragmentation-based MP2 and CCSD(T) energetic calculations.
• Use of aug-cc-pVNZ basis sets (N=T, Q, 5) with approximately 6200 basis functions.
• Development and application of in-house fragment-based algorithms (REAlgo and CIC).

Main Results:

• Accurate energy calculations were performed on a 20-water cage clathrate system.
• Vibrational infrared (IR) spectra were computed and analyzed.
• The complete basis set (CBS) limit at the CCSD(T) level was achieved for this system size, a first for this scale.

Conclusions:

• Fragmentation-based methods enable high-level correlated calculations on large systems.
• These computational approaches are practical on standard hardware (e.g., desktop workstations).
• This work opens new possibilities for studying intermolecular interactions in complex molecular clusters.