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Title: Electronically coarse grained molecular model of water
Author: Cipcigan, Flaviu Serban
ISNI:       0000 0004 7232 1209
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2017
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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.
Supervisor: Ackland, Graeme Sponsor: Engineering and Physical Sciences Research Council (EPSRC)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: transferable water model ; coarse grained model ; supercooled water ; supercritical water ; ice II ; hydrogen bonding ; liquid-vapour interface ; molecular dynamics ; water ; path integral