A molecular dynamics study of the far infrared spectrum of liquid water

Guillot, B.

doi:10.1063/1.461069

Cited by 185 publications

(123 citation statements)

References 40 publications

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“…78,87 For the dipole moment, the permanent term contributes 87− 88%, while the induced term contributes 0.5−1.2%. For the polarizability, the contributions of the permanent and the induced terms are approximately 4−5% and 80%, respectively.…”

Section: Resultsmentioning

confidence: 99%

Effect of Ion Pairing on the Solution Dynamics Investigated by the Simulations of the Optical Kerr Effect and the Dielectric Relaxation Spectra

Zhang

Zhuang

2013

J. Phys. Chem. B

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ABSTRACT:The optical Kerr effect (OKE) and dielectric relaxation spectroscopy (DRS) signals of MgCl 2 aqueous solutions were modeled based on the same group of molecular dynamics simulation trajectories. Plausible agreement between the simulations and the experiments allows us to analyze the microscopic origin of the different concentration dependences of relaxation times probed by these two techniques. Our simulations suggest that a significant amount of cations and anions associate in the solutions due to the ion pairing effect. These ion assemblies as well as the free cations form suspending clusters together with the water molecules in their cation hydration shells. The dynamics of water molecules in these clusters is significantly hindered, while that of other water molecules remains largely unaffected. The relaxation times measured by OKE and DRS have different concentration dependences because DRS probes only the rotational dynamics of water molecules outside of the cluster while OKE contains the information of dynamics of all of the water molecules in the solutions. Such findings provide us a microscopic picture on how the ion hydration affects the water dynamics in certain ionic solutions in which ion pairing plays an important role.

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Section: Resultsmentioning

confidence: 99%

Effect of Ion Pairing on the Solution Dynamics Investigated by the Simulations of the Optical Kerr Effect and the Dielectric Relaxation Spectra

Zhang

Zhuang

2013

J. Phys. Chem. B

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“…Unfortunately, there exist a large variety of different suggestions which are discussed in detail, for example, by Gaigeot and Sprik 33 who also compare IR spectra obtained with different choices. We consider here the 'standard' quantum correction factor 2/(1 þ exp(Àho/2pk B T), 33,34 which results in…”

Section: Computationsmentioning

confidence: 99%

“…It has previously been applied in calculations of the far and mid-IR spectra of liquid water 32,34 and crystals. 35 In addition, comparison will be made with the so-called 'harmonic' quantum correction factor ho/2pk B T/(1 À exp(Àho/2pk B T) which yields…”

Section: Computationsmentioning

confidence: 99%

Environmental effects on vibrational proton dynamics in H₅O₂⁺: DFT study on crystalline H₅O₂⁺ClO₄⁻

Vener

Sauer

2005

Phys. Chem. Chem. Phys.

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The structure as well as IR and inelastic neutron scattering (INS) spectra of H 5 O 2 1 in crystalline H 5 O 2 1 ClO 4 À were simulated using Car-Parrinello molecular dynamics with the BLYP functional. The potential of the OÁ Á ÁH 1 Á Á ÁO fragment is very shallow. The Pnma structure, assumed in the X-ray study to be the most suitable choice, is a saddle point on the potential energy surface, while the P2 1 2 1 2 1 minimum structure is only 20 cm À1 lower in energy. The computed INS and IR spectra enable us to achieve a complete assignment of the observed spectra. The broad band between 1000 and 1400 cm À1 is due to the asymmetric stretch and one of the bending vibrations of the OÁ Á ÁH 1 Á Á ÁO fragment, while the band between 1600 and 1800 cm À1 is due to the bending vibration of the water molecules and the second bending of the OÁ Á ÁH 1 Á Á ÁO fragment. Comparison with the vibrational spectra of isolated H 5 O 2 1 , obtained using Born-Oppenheimer molecular dynamics simulation, reveals environmental effects on vibrational proton dynamics in strong H-bonded species. The most pronounced changes are found for the OÁ Á ÁH 1 Á Á ÁO bending modes because the two bending coordinates become distinctly different for the structure that the H 5 O 2 1 ion assumes in the crystal.

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“…The vector M(t) is the total dipole moment of the simulation cell at a time t. The method of computing IR opacities by the means of molecular dynamics simulations has been used in the past, for instance for calculation of IR spectrum of water (Silvestrelli et al 1997;Iftimie & Tuckerman 2005;Guillot 1991). We note that the real absorption coefficient that is used in the modeling is given by α(ω)/n(ω), where n(ω) is the index of refraction, because an atmosphere of a cool, helium-rich white dwarf is a refractive medium (Kowalski & Saumon 2004).…”

Section: Computational Approachmentioning

confidence: 99%

“…The IR spectrum is represented by the frequency-dependent absorptivity coefficient, α(ω), that was computed through the Fourier transform of the dipole moment time autocorrelation function (Guillot 1991;Silvestrelli et al 1997;Jahn & Kowalski 2014) as…”

Section: Computational Approachmentioning

confidence: 99%

Infrared absorption of dense helium and its importance in the atmospheres of cool white dwarfs

Kowalski

2014

A&A

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Aims. Hydrogen-deficient white dwarfs are characterized by very dense, fluid-like atmospheres of complex physics and chemistry that are still poorly understood. The incomplete description of these atmospheres by the models results in serious problems with the description of spectra of these stars and subsequent difficulties in derivation of their surface parameters. Here, we address the problem of infrared (IR) opacities in the atmospheres of cool white dwarfs by direct ab initio simulations of IR absorption of dense helium.Methods. We applied state-of-the-art density functional theory-based quantum molecular dynamics simulations to obtain the time evolution of the induced dipole moment. The IR absorption coefficients were obtained by the Fourier transform of the dipole moment time autocorrelation function. Results. We found that a dipole moment is induced due to three-and more-body simultaneous collisions between helium atoms in highly compressed helium. This results in a significant IR absorption that is directly proportional to ρ 3 He , where ρ He is the density of helium. To our knowledge, this absorption mechanism has never been measured or computed before and is therefore not accounted for in the current atmosphere models. It should dominate the other collisionally induced absorptions (CIA), arising from H−He and H 2 −He pair collisions, and therefore shape the IR spectra of helium-dominated and pure helium atmosphere cool white dwarfs for He/H > 10 4 . Conclusions. Our work shows that there exists an unaccounted IR absorption mechanism arising from the multi-collisions between He atoms in the helium-rich atmospheres of cool white dwarfs, including pure helium atmospheres. This absorption may be responsible for a yet unexplained frequency dependence of near-and mid-IR spectra of helium-rich stars.

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A molecular dynamics study of the far infrared spectrum of liquid water

Cited by 185 publications

References 40 publications

Effect of Ion Pairing on the Solution Dynamics Investigated by the Simulations of the Optical Kerr Effect and the Dielectric Relaxation Spectra

Effect of Ion Pairing on the Solution Dynamics Investigated by the Simulations of the Optical Kerr Effect and the Dielectric Relaxation Spectra

Environmental effects on vibrational proton dynamics in H₅O₂⁺: DFT study on crystalline H₅O₂⁺ClO₄⁻

Infrared absorption of dense helium and its importance in the atmospheres of cool white dwarfs

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A molecular dynamics study of the far infrared spectrum of liquid water

Cited by 185 publications

References 40 publications

Effect of Ion Pairing on the Solution Dynamics Investigated by the Simulations of the Optical Kerr Effect and the Dielectric Relaxation Spectra

Effect of Ion Pairing on the Solution Dynamics Investigated by the Simulations of the Optical Kerr Effect and the Dielectric Relaxation Spectra

Environmental effects on vibrational proton dynamics in H5O2+: DFT study on crystalline H5O2+ClO4−

Infrared absorption of dense helium and its importance in the atmospheres of cool white dwarfs

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Environmental effects on vibrational proton dynamics in H₅O₂⁺: DFT study on crystalline H₅O₂⁺ClO₄⁻