Ackland, Graeme

Cipcigan, Flaviu Serban

Engineering and Physical Sciences Research Council (EPSRC)

2018-03-15T11:53:17Z

2018-03-15T11:53:17Z

2017-07-10

Electronic coarse graining is a technique improving the predictive power of molecular dynamics simulations by representing electrons via a quantum harmonic oscillator. This construction, known as a Quantum Drude Oscillator, provides all molecular long-range responses by uniting many-body dispersion, polarisation and cross interactions to all orders. To demonstrate the predictive power of electronic coarse graining and provide insights into the physics of water, a molecular model of water based on Quantum Drude Oscillators is developed. The model is parametrised to the properties of an isolated molecule and a single cut through the dimer energy surface. Such a parametrisation makes the condensed phase properties of the model a prediction rather than a fitting target. These properties are studied in four environments via two-temperature adiabatic path integral molecular dynamics: a proton ordered ice, the liquid{vapour interface, supercritical and supercooled water. In all these environments, the model predicts a condensed phase in excellent agreement with experiment, showing impressive transferability. It predicts correct densities and pressures in liquid water from 220 K to 647 K, and a correct temperature of maximum density. Furthermore, it predicts the surface tension, the liquid-vapour critical point, density of ice II, and radial distribution functions across all conditions studied. The model also provides insight into the relationship between the molecular structure of water and its condensed phase properties. An asymmetry between donor and acceptor hydrogen bonds is identified as the molecular scale mechanism responsible for the surface orientation of water molecules. The dipole moment is identified as a molecular scale signature of liquid-like and gas-like regions in supercritical water. Finally, a link between the coordination number and the anomalous thermal expansion of the second coordination shell is also presented.

http://hdl.handle.net/1842/28814

en

The University of Edinburgh

Flaviu S. Cipcigan, Vlad P. Sokhan, Andrew P. Jones, Jason Crain, and Glenn J. Martyna. Hydrogen bonding and molecular orientation at the liquid{vapour interface of water. Phys. Chem. Chem. Phys., 17(14):8660{ 8669, 2015. doi: 10.1039/c4cp05506c.

Flaviu S. Cipcigan, Vlad P. Sokhan, Jason Crain, and Glenn J. Martyna. Electronic coarse graining enhances the predictive power of molecular simulation allowing challenges in water physics to be addressed. J. Comput. Phys., 326:222{233, 2016. doi: 10.1016/j.jcp.2016.08.030.

A. Jones, F. Cipcigan, V. P. Sokhan, J. Crain, and G. J. Martyna. Electronically coarse-grained model for water. Phys. Rev. Lett., 110(22), 2013. doi: 10.1103/physrevlett.110.227801.

A. P. Jones, J. Crain, F. S. Cipcigan, V. P. Sokhan, M. Modani, and G. J. Martyna. Electronically coarse-grained molecular dynamics using quantum drude oscillators. Mol. Phys., 111(22-23):3465{3477, 2013. doi: 10.1080/ 00268976.2013.843032.

V. P. Sokhan, A. Jones, F. S. Cipcigan, J. Crain, and G. J. Martyna. Molecular-scale remnants of the liquid-gas transition in supercritical polar uids. Phys. Rev. Lett., 115(11), 2015. doi: 10.1103/physrevlett.115.117801.

Vlad P. Sokhan, Andrew P. Jones, Flaviu S. Cipcigan, Jason Crain, and Glenn J. Martyna. Signature properties of water: Their molecular electronic origins. Proc. Natl. Acad. Sci. U.S.A., 112(20):6431{6346, 2015. doi: 10. 1073/pnas.1418982112.

transferable water model

coarse grained model

supercooled water

supercritical water

ice II

hydrogen bonding

liquid-vapour interface

molecular dynamics

water

path integral

Electronically coarse grained molecular model of water

Thesis or Dissertation

Doctoral

PhD Doctor of Philosophy