Sameindalýsing á vatni / Molecular Modelling of Water - verkefni lokið
Fréttatilkynning verkefnisstjóra
In this project a transferable interaction potential for water molecules has been developed. The potential is based on a single-center multipole expansion (SCME) of the electrostatic interactions, and although many interaction potentials for water have previously been developed, the SCME model is unique in that the multipole expansion is carried out all the way up to the hexadecapole moment.
In this project a transferable interaction potential for water molecules has been developed. The potential is based on a single-center multipole expansion (SCME) of the electrostatic interactions, and although many interaction potentials for water have previously been developed, the SCME model is unique in that the multipole expansion is carried out all the way up to the hexadecapole moment. Moreover, both dipole and quadrupole moments are polarizable. Other components of the interaction energy, i.e. the dispersion interactions and short-range exchange-repulsion, are described by parameters that have been fit to highly accurate quantum chemistry calculations. Although all parameters of SCME are derived from properties of a single H2O molecule, an accurate description of water clusters and condensed phases of water (liquid, ice) emerges naturally from the underlying molecular description. The SCME model has also been extended by a short-range machine-learning potential to correct remaining inaccuracies in the description of quantum mechanical effects related to the overlap of molecular charge densities at short intermolecular separations. With this improvement, the extended SCME model promises to become a universal interaction potential for water of unprecedented accuracy.
Heiti verkefnis: Sameindalýsing
á vatni / Molecular Modelling of Water
Verkefnisstjóri: Kjartan Thor Wikfeldt, Raunvísindastofnun Háskólans
Tegund styrks: Rannsóknastöðustyrkur
Styrkár: 2012-2014
Fjárhæð styrks: 18,17 millj. kr.
Tilvísunarnúmer Rannís: 12004404
Molecular simulations of
water using other interaction potentials for water were also performed during
the project to shed light on the unusual properties of liquid water and ambient
and supercooled temperature. First, a deeper understanding of triplet correlations,
i.e. statistical correlations between three water molecules, was obtained using
various simulation methods, and future experiments were suggested to determine
what role such correlations actually play in liquid water. Second, simulations
of water were applied to assist in the interpretation of groundbreaking
free-electron laser experiments which probed, for the first time, the molecular
structure of water down to 227 K, which is below the homogenous nucleation
temperature. Third, the detailed nature of isotope substitution effects in
water (replacing H atoms with D atoms) was elucidated by interpreting inelastic
x-ray scattering experiments by means of molecular simulations. Finally, a
puzzling dynamical feature, called the boson peak, was discovered in
simulations of deeply supercooled liquid water, suggesting a connection of the
boson peak with the hypothesized liquid-liquid transformation in supercooled
water.
In the future, the SCME interaction potential for water molecules, and in particular its extended version with a machine-learning potential, will be applied in predictive simulations of liquid water under various conditions as well as of different ice phases and ice surfaces. These simulations will be able to shed light on some of the remaining mysteries of liquid water and ice. Primary applications include deeply supercooled liquid water, where the existence of a liquid-liquid phase transition has been inferred but not yet proven, as well as the surface of ice under various atmospheric conditions, since the surface structure is still poorly understood despite its fundamental importance to various molecular processes in Earth's atmosphere.
Scientific publications resulting from the project
1. K. T. Wikfeldt, E. R. Batista, F. D Vila, and H. Jónsson. A transferable H2O interaction potential based on a single center multipole expansion: SCME. Phys. Chem. Chem. Phys., 15:16542–16556, 2013.
2. D. Dhabal, M. Singh, K. T. Wikfeldt, and C. Chakravarty. Triplet correlation functions in liquid water. J. Chem. Phys., 141:174504, 2014.
3. J. A. Sellberg, C Huang, T. A. McQueen, N. D. Loh, H. Laksmono, D. Schlesinger, R. G. Sierra, D. Nordlund, C. Y. Hampton, D. Starodub, D. P. DePonte, M. Beye, C. Chen, A. V. Martin, A. Barty, K. T. Wikfeldt, T. M. Weiss, C. Caronna, J. Feldkamp, L. B. Skinner, M. M. Seibert, M. Messerschmidt, G. J. Williams, S. Boutet, L. G. M. Pettersson, M. J. Bogan and A. Nilsson. Ultrafast x-ray probing of water structure below the homogeneous ice nucleation temperature. Nature, 510:381–384, 2014.
4. Y. Harada, T. Tokushima, Y. Horikawa, O. Takahashi, H. Niwa, M. Kobayashi, M. Oshima, Y. Senba, H. Ohashi, K. T. Wikfeldt, et al. Selective probing of the OH or OD stretch vibration in liquid water using resonant inelastic soft-x-ray scattering. Phys. Rev. Lett., 111:193001, 2013.
5. E. M. McIntosh, K. T. Wikfeldt, J. Ellis, A. Michaelides, and W. Allison. Quantum effects in the diffusion of hydrogen on Ru (0001). J. Phys. Chem. Lett., 4:1565, 2013.
6. P. Kumar, K. T. Wikfeldt, D. Schlesinger, L. G. M. Pettersson, and H. E. Stanley. The Boson peak in supercooled water. Nature Sci. Rep., 3:1980, 2013.
