In this project Ab Initio Molecular Dynamics (AIMD) and statistical mechanics were used to study the structural and dynamical properties of pure water at ambient conditions. A generalized gradient approximations (GGA) exchange-correlation (XC) functional Perdew-Burke-Ernzerhof (PBE) and van der Waals Density Functional (vdW-DF) XC functionals were used to describe the system with and without van der Waals and many body corrections (MBC). Here we present the impact of these approximations on properties such as the radial distribution functions, tetrahedrality parameters, hydrogen bond angles, and the average number of hydrogen bonds in the system.

1. Abstract
• In this project Ab Initio Molecular Dynamics (AIMD) and statistical
mechanics were used to study the structural and dynamical properties of pure
water at ambient conditions. A generalized gradient approximations (GGA)
exchange-correlation (XC) functional Perdew-Burke-Ernzerhof (PBE) and
van der Waals Density Functional (vdW-DF) XC functionals were used to
describe the system with and without van der Waals and many body
corrections (MBC). Here we present the impact of these approximations on
properties such as the radial distribution functions, tetrahedrality parameters,
hydrogen bond angles, and the average number of hydrogen bonds in the
system.
Simulation Methods and Conditions
• Liquid water at 300 K was modeled by using a
32 molecule cubic box at equilibrium density
using periodic boundary conditions.
• AIMD simulations were performed using the
VASP code with interatomic forces derived
from DFT.
• PBE and vdW-DF XC functionals
• Corrections to DFT using a many body
decomposition of the energy and accurate
coupled-cluster results for small clusters in the
many body expansion.
Preliminary Results
Acknowledgements
• DoE SULI Program and CCMS Program
• Equations of State and Quantum Simulations Group at LLNL
• All of my colleagues from the CCMS summer student program.
• My mentor, Dr. Miguel Morales-Silva, Universidad del Turabo, CMMD,
and Dr. Tony Baylis for giving me the tools and confidence for success.
Future Work
• Study what different competing forces may be missing in functional
correlations.
• Take into account quantum nuclear effects using Path Integral
method.
References
• Ph. Wernet et. al., Science 304, 995 (2004).
• L. Skinner et al., J. Chem. Phys.138, 074506 (2013).
• R. DiStasio et. al., J. Chem. Phys. 121. 141, 084502 (2014).
• E. Schwegler et. al., J. Chem. Phys, 5400 (2004).
• M. Dion et. al., Phys. Rev. Lett. 92, 24 (2004).
• A. Møgelhø et. al., J. Phys. Chem. 115, 24 (2004).
• M. Ceriotti et al., PNAS. 110, 39 (2013).
Introduction
Discussion
FIGURE 1. 32 Water molecules in a
10 x10x 10Å box.
TABLE I. Tabulated comparison of the structural properties of liquid water for PBE
and vdW-DF XC functionals. All simulations were conducted using the details described
in the methods section.
• In agreement with past literature, the addition of vdW/dispersion
corrections to the correlation term in DFT softens the first peak in
the g(r)O-O (Figure 2).
• Adding MBC to PBE and vdW-DF demonstrate opposite trends. In
figure 2, PBE-D3-MBC in respect to PBE-D3 is softened but for
vdW-DF-MBC in respect to vdW-DF it becomes more structured.
Figures 3 and 4 also follow this trend.
• These results demonstrate that other competing forces have not
been taken into account when describing liquid water.
Plays a crucial role in:
• Biological processes such as photosynthesis and
cellular respiration
• Considered a universal solvent
Ubiquitous Liquid:
• The Structure of pure liquid water at ambient conditions
is still unknown experimentally and cannot be
reproduced theoretically
• Currently there are two classes of models for liquid
water that are still under debate.
First Principles Simulations of Liquid Water: van der Waals and Many Body Corrections
Svetlana Gelpi-Domínguez1,2, Tuan Ahn Pham3, Miguel A. Morales-Silva3
1)Escuela de Ciencias y Tecnología, Universidad del Turabo, Gurabo, 00778, P.R.
2)Department of Chemistry, University of Connecticut, Storrs, 06269, CT
3)Lawrence Livermore National Laboratory, Livermore, 94550, CA
Method
r(Å)1
Max
g(r)1
Max
r(Å)1
Min
g(r)1
Min
r(Å)2
Max
g(r)2
Max
nHB
PBE
2.74
3.54
3.23
0.38
4.41
1.50
3.66
PBE-D3
2.71
3.67
3.25
0.39
4.32
1.45
3.70
PBE-D3-MBC
2.75
3.47
3.23
0.513
4.44
1.36
3.57
vdW-DF
2.91
2.29
3.44
1.17
----
----
2.71
vdW-DF-MBC
2.71
2.99
3.37
0.77
4.48
1.24
3.37
Experiment
2.8
2.57
3.45
0.84
4.50
1.12
----
FIGURE 2. Radial distribution functions for the
Oxygen-Oxygen pair correlation for PBE and vdW-DF.
FIGURE 3 AND 4. The left column shows a comparison between the distribution and
of Q-parameter in the PBE and vdW-DF simulation. The right column shows a
comparison of the the distribution for the hydrogen angle criteria proposed by Anders et
al. in PBE and vdW-DF .
Variables:
• g(r)- Probability of finding that oxygen pair at a
certain length
• P(Q)- Probability of meeting the Q criteria
(tetrahedrality of the system)
• Fβ(β)[deg-1]- Probability that a molecule meets
Anders et al. hydrogen bond criteria.
What is radial distribution function?
This work performed under the auspices of the U.S. Department of Energy and an appointment to the Office of Science, Science Undergraduate Laboratory Internship (SULI) Program at the Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0 10 20 30 40 50
fβ(β)[deg
-1
]
β[deg]
Hydrogen Bond Angle
PBE
PBE-D3
PBE-D3-MBC
Experimental
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0 10 20 30 40 50
fβ(β)[deg
-1
]
β[deg]
Hydrogen Bond Angle
vdW-DF
vdW-DF-Mono-Dimer
Experimental
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0.009
0 0.2 0.4 0.6 0.8 1
P(Q)
Q
Tetrahedrality
PBE
PBE-D3
PBE-D3-MBC
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0.009
0 0.2 0.4 0.6 0.8 1
P(Q)
Q
Tetrahedrality
vdW-DF
vdW-DF-MBC
0
0.5
1
1.5
2
2.5
3
3.5
4
2.5 3 3.5 4 4.5 5
goo(r)
r[Å]
Pair Correlation
PBE
PBE−D3
PBE−D3−MBC
Experimental
0
0.5
1
1.5
2
2.5
3
3.5
4
2.5 3 3.5 4 4.5 5
goo(r)
r[Å]
Pair Correlation
vdW−DF
vdW−DF−MBC
Experimental