Title:	Putting pressure on clathrate hydrates – new insight into the hydration structure of small molecules
DNr:	SNIC 2019/3-521
Project Type:	SNIC Medium Compute
Principal Investigator:	Ulrich Häussermann <ulrich.haussermann@mmk.su.se>
Affiliation:	Stockholms universitet
Duration:	2019-12-01 – 2020-12-01
Classification:	10404 10403
Homepage:	http://www.mmk.su.se
Keywords:

Abstract

This project is meant to support experimental efforts in the elucidation of the high pressure behavior of clathrate hydrates (CHs), which are crystalline inclusion compounds in which water forms a host that encapsulates small concentrations of guest molecules. CHs occur widely in nature, with e.g. methane and other small hydrocarbon molecules as guests. Despite the enormous environmental impact and potential gas storage properties of CHs, the molecular level interaction between guest species in the cages and the surrounding water network remains poorly understood. These interactions are particularly sensitive to density and therefore pressure is an important variable for probing intermolecular interaction potentials and hydration structures of guest molecules. Our ongoing neutron diffraction experiments concern CHs with the noble gases Ne, Ar, Kr, Xe, and the molecules THF and H2 as guests and are performed in the p,T range 0 – 7 GPa and 90 – 230 K. From these experiments we can extract pressure-induced changes in H bonding interactions, which frequently lead to amorphization of the CH. We want to apply computational methods for help interpreting our experimental data and, vice versa, use experimental data for benchmarking and calibrating modeling methods. Crystalline CHs will be subjected to periodic ab inito DFT calculations using the QUANTUM ESPRESSO package. The results on total energy and electron density distributions will allow to extract optimal guest-water interaction potentials for implementation in the classical MD simulations. Classical MD simulations will be carried out in the isothermal-isobaric NPT ensemble on simulation cells with various sizes, using standard MD packages, particularly GROMACS or LAMMPS. The MD simulations are expected to predict pressure induced crystal structure changes and amorphization and decomposition processes of the CHs within the targeted p,T range.