Can gas hydrate structures be described using classical simulations?

Area of Science:

• Computational chemistry
• Materials science
• Physical chemistry

Background:

• Hydrate solid structures are crucial in various scientific domains.
• Understanding the role of nuclear quantum effects (NQE) in hydrate properties is essential.
• Accurate modeling of water's condensed phases requires considering quantum mechanical behaviors.

Purpose of the Study:

• To investigate the impact of NQE on hydrate solid structures using quantum path-integral simulations.
• To compare the performance of the TIP4PQ/2005 model (for quantum simulations) with the TIP4P/2005 model (for classical simulations).
• To determine the conditions under which classical simulations are sufficient for hydrate studies.

Main Methods:

• Performing quantum path-integral simulations with the TIP4PQ/2005 model.
• Conducting classical simulations using both TIP4PQ/2005 and TIP4P/2005 models.
• Comparing simulation results to analyze the influence of NQE on hydrate properties.

Main Results:

• NQE significantly modify hydrate structure, densities, and energies.
• Classical simulations accurately predict densities above 150 K and relative stabilities with ice I(h).
• The phase diagram of water at negative pressures remains largely unchanged by NQE, with transition pressures showing minimal impact.

Conclusions:

• NQE are crucial for accurate simulations of hydrate densities below 150 K, sublimation energies, heat capacity, and radial distribution functions.
• Classical simulations offer reasonable accuracy for phase diagram predictions of hydrates.
• The TIP4PQ/2005 model provides a more comprehensive description of hydrates when NQE are considered significant.