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Electronically coarse grained waterAndrew Jones, Flaviu Cipcigan, Vlad Sokhan, Jason Crain, Glenn Martyna
A. Jones, F. Cipcigan, V. Sokhan, J. Crain, G. Martyna, Electronically coarse grained model for water, PRL 110, 227801 (2013)
A. Jones, Quantum drude oscillators for accurate many-body intermolecular forces, PhD thesis, The University of Edinburgh
Challenge: extending the transferability of empirical potentialsOur solution: coarse grained electronic structure
Free parameters
Response
1. Quantum Drude Oscillator (QDO) Light negative particle tethered harmonicallyto heavy positive, oppositely charged nucleus
: reduced mass : spring constant : charge
Polarisation:
Dispersion:
…
2. Invariants predicted by QDOs
Polarisation: Dispersion:
H Li K RbCs
1.5
0.5
1.0
1.5
0.5
1.0
1.5
0.5
1.0
He Ne Ar Kr Xe
CH4
H2O
H LiK Rb Cs
He Ne Ar Kr Xe
BH3 CH4 NH3 H2O
= 0.3656 amu
= 0.6287
= -1.1973 e
3. QDO-water model
Frame: ground state moments
QDO: molecular response
+ 0.605 e
- 1.21 e
0.2667 Å0.9572 ÅO
H
M
H 104.52º
4. QDO-water model (continued)
Short range interactions
Repulsion
Electrostatic damping Gaussian charges
5. Efficient sampling: APIMD-QDO
1. Write partition function of N particles as path integral, P slices
2. Define effective (classical) potential of N×P particles
3. Approximate resulting high temperature density matrices
(Adiabatic Path Integral Molecular Dynamics applied to QDOs)
6 . Liquid QDO-water
Radial distribution function Vapour pressure
exp: 43.91 kJ/mol
r / Å2 3 4 5 6 7
g OO(r
)
0.0
0.5
1.0
1.5
2.0
2.5Skinner et al. (exp).Exp. (Soper)QDO, N = 300
46 ± 2 kJ / mol
Dielectric constant
exp: 7879 ± 2
Surface tension
exp: 71.73 mN / m72.6 ± 1 mN / m
Density and dipole moment Electronic distribution
7 . Liquid–vapour interface (unoptimised model)
(ground state distribution substracted)
1 Å
13 Å
15 Å
Dip
ole M
om
ent ±
1σ (D
ebye)
Den
sity
± 1σ
(kg
m
)-3
0
200
400
600
800
1000
1 5 10 15 20 13
1.855
2.6
charge loss
charge gain
Surface charge density
8 . Liquid–vapour interface (continued)
1 5 10 15 20 13
Distance from centre (Å)
-1.0
-0.5
0
0.5
1.0Su
rfac
e ch
arge
± 1σ
(e /
Å3 ×
10
-3)
Surface expansion of nearest neighbour distance by 1–2%
9 . Liquid–vapour interface (continued)
2.7
2.75
2.8
2.85
2.9
2.95
3
O-O
dis
tan
ce (Å
)
surfacebulkhydrogen bonded
neighbours
(only classical model with a surface expansion)
neighbours in shell of radius 3.5 Å
nearest neighbour only
Weaker hydrogen bond at the surface
10 . Liquid–vapour interface (continued)
The hydrogen bond forms in the valleys of the PMF (Potential of Mean Force)
How are hydrogen bonds broken?
11 . Liquid–vapour interface (continued)
2 Acceptor: 16%
2 Donor: 4%
1 Donor: 80%
charge loss
charge gain
neighbour oxygen
Tetrahedrality Number of hydrogen bonds
12 . Liquid–vapour interface (continued)
0
0.5
1
1.5
2
2.5
-1 -0.5 0 0.5 1
p(q
)
q
BulkSurface
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 1 2 3 4 5
bulk
surface
Number of hydrogen bondsFr
actio
n of
mol
ecul
es
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