A Surface-Specific Isotope Effect in Mixtures of Light and Heavy Water

Liu, Jian; Andino, Richard S.; Miller, Christina M.; Chen, Xin; Wilkins, David M.; Ceriotti, Michele; Manolopoulos, David E.

doi:10.1021/jp311986m

Cited by 62 publications

(81 citation statements)

References 56 publications

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“…Although the competition between intra-and intermolecular quantum effects that appears to be ubiquitous in water reduces the impact of neglecting NQEs on average properties (9,25,32,33), the protons should always be treated as quantum particles in studies aimed at capturing rare events or, more generally, properties that depend on the tail of the equilibrium distribution. For instance, a recent study (34) suggests that conflicting interpretations of the X-ray absorption spectroscopy of water (35,36) can be reconciled based on the presence of asymmetrical configurations of HBs in water.…”

Section: Discussionmentioning

confidence: 99%

Nuclear quantum effects and hydrogen bond fluctuations in water

Ceriotti

Cuny

Parrinello

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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The hydrogen bond (HB) is central to our understanding of the properties of water. However, despite intense theoretical and experimental study, it continues to hold some surprises. Here, we show from an analysis of ab initio simulations that take proper account of nuclear quantum effects that the hydrogen-bonded protons in liquid water experience significant excursions in the direction of the acceptor oxygen atoms. This generates a small but nonnegligible fraction of transient autoprotolysis events that are not seen in simulations with classical nuclei. These events are associated with major rearrangements of the electronic density, as revealed by an analysis of the computed Wannier centers and 1 H chemical shifts. We also show that the quantum fluctuations exhibit significant correlations across neighboring HBs, consistent with an ephemeral shuttling of protons along water wires. We end by suggesting possible implications for our understanding of how perturbations (solvated ions, interfaces, and confinement) might affect the HB network in water.path integral molecular dynamics | generalized Langevin equation thermostat | ab initio liquid water D espite its apparent simplicity, liquid water exhibits a number of anomalous properties, such as a decrease in density on freezing, an isobaric density maximum, and its unusually high dielectric constant and heat capacity (1). These, together with its unquestionable importance for climate and life on Earth, have made this substance a subject of intense research by both experiments and simulations.The central concept that has been used to rationalize the peculiar behavior of water is that of the hydrogen bond (HB) (2). The nature of this bond in water has been studied in depth by atomistic computer simulations, which have investigated how it is affected by ionic and electronic polarizability (3, 4), pressure and temperature (5, 6), and nuclear quantum effects (NQEs) (7-9). Furthermore, ab initio molecular dynamics (MD) simulations have been used to shed light on autoionization (10, 11), a process with profound implications for the chemistry of aqueous solutions.In this paper, we investigate the impact of NQEs on the HB in pure water, finding a qualitative increase in fluctuations that leads to a partial dissociation of the covalent O-H bond. The weakening of this covalent bond in the presence of hydrogen bonding is consistent with the red shift of the stretching mode of water upon condensation, as well as with recent experiments demonstrating that selectively exciting the O-H stretch in water leads to a pronounced delocalization of the proton toward the acceptor oxygen atom (12). However, the role of NQEs in governing the extent of this delocalization has not been investigated before now.Our analysis is based on MD simulations of water at different thermodynamic state points, with an ab initio description of the interactions among the nuclei. We also account fully for the quantum nature of the nuclear motion, using a recently developed combination of imaginary time path i...

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Section: Discussionmentioning

confidence: 99%

Nuclear quantum effects and hydrogen bond fluctuations in water

Ceriotti

Cuny

Parrinello

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

228

260

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“…Now, let us consider how the direct estimators can be used in a setting in which one cannot define a clear-cut distinction between the A and B states, but has just one system described by a potential V , and the two states are different regions of configuration space, that are associated to two characteristic functions θ A (q) and θ B (q), which are one if the configuration can be ascribed to one of the states, and zero otherwise. For instance, the functions could select configurations in which the tagged atom is at a given distance from an interface [62], or in a specific hydrogen-bonding environment.…”

Section: Discussionmentioning

confidence: 99%

Direct path integral estimators for isotope fractionation ratios

Cheng¹,

Ceriotti²

2014

The Journal of Chemical Physics

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Fractionation of isotopes among distinct molecules or phases is a quantum effect which is often exploited to obtain insights on reaction mechanisms, biochemical, geochemical and atmospheric phenomena. Accurate evaluation of isotope ratios in atomistic simulations is challenging, because one needs to perform a thermodynamic integration with respect to the isotope mass, along with time-consuming path integral calculations. By re-formulating the problem as a particle exchange in the ring polymer partition function, we derive new estimators giving direct access to the differential partitioning of isotopes, which can simplify the calculations by avoiding thermodynamic integration. We demonstrate the efficiency of these estimators by applying them to investigate the isotope fractionation ratios in the gas-phase Zundel cation, and in a few simple hydrocarbons.

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“…However,acombined theoretical and experimental study of the free O À H/O À Dg roups at the water-air interface has shown that the bond orientation of the water molecules at this interface depends on the isotopic dilution which is caused by nuclear quantum effects. [137,138] Path integral MD simulations at the waterair interface revealed the preferential orientation of the O À H and O À Dgroups of the HDO molecule.The average orientational angle between the OÀH(O À D) groups and the surface normal is displayed in Figure 13 b. Thes imulated and experimental SFG data confirmed that the OÀHg roup of an HDO molecule is slightly more oriented toward the air and is less inclined to engage in hydrogen bonds with other water molecules (Figure 13 c). These give rise to the zero-point energy of the vibrational mode,influencing the hydrogen-bonding strength in ac omplex manner.N uclear quantum effects are particularly relevant for the interface,b ecause the vibrational energy difference between the free OÀHand hydrogen-bond O À Hstretch mode is comparable to kT at room temperature.…”

Section: Nuclear Quantum Effectsmentioning

confidence: 99%

Molecular Structure and Dynamics of Water at the Water–Air Interface Studied with Surface‐Specific Vibrational Spectroscopy

2015

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Water interfaces provide the platform for many important biological, chemical, and physical processes. The water-air interface is the most common and simple aqueous interface and serves as a model system for water at a hydrophobic surface. Unveiling the microscopic (<1 nm) structure and dynamics of interfacial water at the water-vapor interface is essential for understanding the processes occurring on the water surface. At the water interface the network of very strong intermolecular interactions, hydrogen-bonds, is interrupted and the density of water is reduced. A central question regarding water at interfaces is the extent to which the structure and dynamics of water molecules are influenced by the interruption of the hydrogen-bonded network and thus differ from those of bulk water. Herein, we discuss recent advances in the study of interfacial water at the water-air interface using laser-based surface-specific vibrational spectroscopy.

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A Surface-Specific Isotope Effect in Mixtures of Light and Heavy Water

Cited by 62 publications

References 56 publications

Nuclear quantum effects and hydrogen bond fluctuations in water

Nuclear quantum effects and hydrogen bond fluctuations in water

Direct path integral estimators for isotope fractionation ratios

Molecular Structure and Dynamics of Water at the Water–Air Interface Studied with Surface‐Specific Vibrational Spectroscopy

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