77. On the interplay of the potential energy and dipole surfaces in controlling the infrared activity of water.  

      G.R. Medders, F. Paesani, J. Chem. Phys. 142, 212411 (2015). [link]

Here, we disentangle the contributions of the potential energy surface (PES) and dipole moment

surface (DMS) to the infrared spectrum of liquid water by examining three classes of models,

ranging in complexity from simple point charge models to accurate representations of the many-body

interactions. By decoupling the PES from the DMS in the calculation of the infrared spectra, we

demonstrate that the PES, by directly modulating the vibrational structure, primarily controls the

width and position of the spectroscopic features. Due to the dependence of the molecular dipole

moment on the hydration environment, many-body electrostatic effects result in a 100 cm−1 redshift

in the peak of the OH stretch band. While an accurate description of many-body collective motion is

required to generate the correct structure of the liquid, the infrared intensity in the OH stretching region

appears to be a measure of the local structure due to the dominance of the 1B and short-ranged 2B

contributions to the dipole moment.

76. Infrared and Raman spectroscopy of liquid water through “first principles” many-body molecular dynamics.

      G.R. Medders, F. Paesani, J. Chem. Theory Comput. 11, 1145 (2015). [link]

In this study, we present an integrated theoretical and computational framework (named many-body

molecular dynamics or MB-MD) that, by systematically removing uncertainties associated with

existing approaches, enables a rigorous modeling of vibrational spectra of water from quantum

dynamical simulations. Specifically, we extend approaches used to model the many-body expansion

of interaction energies to develop many-body representations of the dipole moment and polarizability

of water. The combination of these “first-principles” representations with centroid molecular dynamics

simulations enables the simulation of infrared and Raman spectra of liquid water under ambient

conditions that, without relying on any ad hoc parameters, are in good agreement with the

corresponding experimental results. Our analysis indicates that MB-MD correctly reproduces both the

shifts and the shapes of the main features of the infrared spectrum of water without requiring any

ad hoc or empirical adjustment.

73. Thermodynamics of water dimer dissociation in the primary hydration shell of the iodide ion with temperature-  

      dependent vibrational predissociation spectroscopy. C.T. Wolke, F.S. Menges, N. Totsch, O. Gorlova,

      J.A. Fournier, G.H. Weddle, M.A. Johnson, N. Helne, T.K. Esser, H. Knorke, K.R. Asmis, A.B. McCoy,

      D.J. Arismendi-Arrieta, R. Prosmiti, F. Paesani, J. Phys. Chem. A 119, 1859 (2015). [link]

The strong temperature dependence of the I−(H2O)2 vibrational predissociation spectrum is traced to the

intracluster dissociation of the ion-bound water dimer into independent water monomers that remain tethered

to the ion. The thermodynamics of this process is determined using van’t Hoff analysis of key features that

quantify the relative populations of H-bonded and independent water molecules. The cause of this reduction

is explored with electronic structure calculations of the potential energy profile for dissociation of the dimer,

which suggest that both reduction of the intrinsic binding energy and vibrational zero-point effects act to weaken

the intermolecular interaction between the water molecules in the first hydration shell.

72. Infrared spectra of HCl(H2O)n clusters from semiempirical Born–Oppenheimer molecular dynamics simulations.

      W. Lin, F. Paesani, J. Phys. Chem. A 119, 4450 (2015). [link]

Infrared spectra of HCl(H2O)n clusters, with n = 4 - 10 and 21, are calculated at T = 50 K from

semiempirical Born–Oppenheimer molecular dynamics simulations performed with the PM3-MAIS

model. The specific focus of this study is on the relationship between spectroscopic features

associated with the presence of the excess proton generated by the HCl dissociation as a function

of n and the underlying water hydrogen-bonding topologies. Vibrational modes involving the motion

of the excess proton are attributed to specific features appearing at ~1175 cm-1 for Zundel-type

structures, in the 1670 - 1800 cm-1 range for intermediate Zundel–Eigen-type structures, and

at ~2820 cm-1 for Eigen-type structures. This broad range of vibrational frequencies correlates

with the position of the excess proton within the clusters. Overall, the theoretical predictions are

in good agreement with the available experimental data.

© Paesani Research Group. All rights reserved.

74. MIL-101(Fe) as a lithium-ion battery electrode material: a relaxation and intercalation mechanism during lithium

      insertion. J. Shin, M. Kim, J. Cirera, S.H. Chen, G. Halder, T.A. Yersak, F. Paesani, S.M. Cohen, Y.S. Meng,

      J. Mater. Chem. A 3, 4738 (2015). [link]

The electrochemical performance of a MIL-101(Fe) MOF as a lithium ion battery electrode is

reported for the first time. Iron metal centers can be electrochemically activated. The Fe3+/Fe2+ redox

couple is electrochemically active, but not reversible over many cycles. A comparison between ex situ

and in operando XAS on the Fe K-edge is presented. Our results indicate that the capacity fade is

related to a time dependent, irreversible oxidation of Fe2+ to Fe3+. These results are key in proving the

importance of in operando XAS measurements. The MOF side reaction with an electrolyte has been

computationally modeled. These results provide further insights on the mechanism responsible for

the MOF lack of reversibility. Future guidelines for improving the reversibility of MOFs as electrodes

in Li-ion batteries based on the fine-tuning of the electronic structure of the material are proposed.

75. Effects of surface pressure on the properties of Langmuir monolayers and interfacial water at model sea-spray

      aerosol surfaces. W. Lin, A.J. Clark, F. Paesani, Langmuir 31, 2147 (2015). [link]

The effects of surface pressure on the physical properties of Langmuir monolayers of palmitic acid (PA)

and dipalmitoylphosphatidic acid (DPPA) at the air/water interface are investigated through molecular

dynamics simulations with atomistic force fields. For PA monolayers at T = 300 K, the untilted condensed

phase with a hexagonal lattice structure is found at high surface pressure, while the uniformly tilted

condensed phase with a centered rectangular lattice structure is observed at low surface pressure,

in agreement with the available experimental data. A state with uniform chain tilt but no periodic spatial

ordering is observed for DPPA monolayers on a Na+/water subphase at both high and low surface

pressures. The analysis of the hydrogen- bonding properties at the monolayer/water interface indicates

that water molecules hydrogen-bonded to DPPA reorient more slowly than those hydrogen-bonded to the

PA head groups, with the orientational dynamics becoming significantly slower at high surface pressure.

78. Water structure and dynamics in homochiral [Zn(l-L)(X)] metal-organic frameworks. Z.L. Terranova, M.M. Agee,

      F. Paesani, J. Phys. Chem. C 119, 18239 (2015). [link]

The structural, thermodynamic, and dynamical properties of water adsorbed in two homochiral MOFs

with general formula [Zn(l-L)(X)] are investigated through MD simulations. Water molecules establish

distinct hydrogen-bonding patterns within the pores of the two MOFs, which directly correlate with

the strength of the underlying framework-water interactions. At low loading, the Zn-Cl groups of

[Zn(l-L)(Cl)] effectively provide a templating scaffold for the formation of one-dimensional

hydrogen-bonded water chains that propagate along the MOF channels following the helicity of the

framework. In contrast, the relatively weaker framework-water interactions in [Zn(l-L)(Br)] lead to

less ordered water distributions inside the pores. The simulation results are in agreement with the

available experimental data and provide molecular-level insights into specific hydrogen-bonding

motifs that can be related to the different proton conductivities measured for the two MOFs.

79. On the representation of many-body interactions in water. G.R. Medders, A.W. Götz, M.A. Morales, P. Bajaj,

      F. Paesani, J. Chem. Phys. 143, 104102 (2015). [link]

Recent work has shown that the many-body expansion of the interactionenergy can be used to

develop analytical representations of global potential energy surfaces (PESs) for water. In this study,

the role of short- and long-range interactions at different orders is investigated by analyzing water

potentials that treat the leading terms of the many-body expansion through implicit (i.e., TTM3-F and

TTM4-F PESs) and explicit (i.e., WHBB and MB-pol PESs) representations. It is found that explicit

short-range representations of 2-body and 3-body interactions along with a physically correct incorporation

of short- and long-range contributions are necessary for an accurate representation of the water

interactions from the gas to the condensed phase. Similarly, a complete many-body representation of the

dipole moment surface is found to be crucial to reproducing the correct intensities of the infrared

spectrum of liquid water.