Vibrational spectra of light and heavy water with application to neutron cross section calculations

Nuclear quantum effects have significant contributions to thermodynamic quantities and structural properties; furthermore, very expensive methods are necessary for their accurate computation. In most calculations, these effects, for instance, zero-point energies, are simply neglected or only taken into account within the quantum harmonic oscillator approximation. Herein, we present a new method, Generalized Smoothed Trajectory Analysis, to determine nuclear quantum effects from molecular dynamics simulations. The broad applicability is demonstrated with the examples of a harmonic oscillator and different states of water. Ab initio molecular dynamics simulations have been performed for ideal gas up to the temperature of 5000 K. Classical molecular dynamics have been carried out for hexagonal ice, liquid water, and vapor at atmospheric pressure. With respect to the experimental heat capacity, our method outperforms previous calculations in the literature in a wide temperature range at lower computational cost than other alternatives. Dynamic and structural nuclear quantum effects of water are also discussed.

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Section: Resultsunclassified

Nuclear Quantum Effects from the Analysis of Smoothed Trajectories: Pilot Study for Water

Berta

Ferenc

Bakó

et al. 2020

J. Chem. Theory Comput.

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“…30 The main peak in hydrogen power spectra at low frequency region is related to the restricted translation of hydrogen bond, and the shoulder is attributed to the bending motion of the O−O−O angle, 28 which can also be confirmed from the strongest peak in oxygen power spectra at round 50 cm −1 . For the hydrogen power spectrum arising from the bending vibration in light water, the peak predicted by ReaxFF (∼1900 cm −1 ) shows a blue shift compared to the classical and CPMD calculations (<1800 cm −1 ), 29,31 indicating that the H−O−H angle of water molecule in ReaxFF is slightly more rigid. The similarity is also observed in heavy water due to the same H−O−H angle parameters as light water.…”

mentioning

confidence: 84%

Isotope Effects in Water: Differences of Structure, Dynamics, Spectrum, and Proton Transport between Heavy and Light Water from ReaxFF Reactive Force Field Simulations

Zhang

Chen

Duin

2018

J. Phys. Chem. Lett.

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Investigating properties of both heavy and light water at the atomistic level is essential to understanding chemical and biological processes in aqueous solution. However, appropriately describing their difference on the nanoscale is still challenging. Employing ReaxFF reactive molecular dynamics simulations, we systematically study the structure, dynamics, and spectra of heavy and light water. With the water force field potential we developed, the different features between heavy and light water can be simulated appropriately by the classical treatment on large size and time scale. Here, we also report the structural difference between DO and HO in bulk heavy/light water. In addition, the diffusion constants of heavy and light water are successfully reproduced, and the Grotthuss hopping mechanism of proton transport in liquid water is properly described as well. It allows us to study a complex system in heavy/light aqueous environments, such as proton transport, chemical reaction, and tracing the reaction mechanism with an isotope substitute.

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“…The density of states (DOS) for both hydrogen and oxygen in light water for the CAB model are used as the input of our calculation [15]. The data, shown in Fig.…”

Section: Evaluation Of the Self-scattering Functionmentioning

confidence: 99%

“…The convolutional discrete Fourier transform (CDFT) method is firstly introduced in section 3, and applied to the Gaussian approximation in section 3.1. Using the identical input as the state-of-the-art CAB light water cross section [9,10], the CDFT calculated scattering function of light water is benchmarked against differential and integral cross sections in section 4. This work is concluded in section 5.…”

Section: Introductionmentioning

confidence: 99%

Convolutional discrete Fourier transform method for calculating thermal neutron cross section in liquids

Du,

Cai

2021

Preprint

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Being exact at both short-and long-time limits, the Gaussian approximation is widely used to calculate neutron incoherent inelastic scattering functions in liquids. However, to overcome a few numerical difficulties, extra physical approximations are often employed to ease the evaluation.In this work, a new numerical method, called convolutional discrete Fourier transform, is proposed to perform Fourier transform of exp[− f (t)]. We have applied this method to compute the differential cross sections of light water up to 10 eV. The obtained results, thoroughly benchmarked against experimental data, showed a much higher dynamic range than conventional fast Fourier transform. The calculated integral cross sections agree closely with the light water data in the state-of-the-art nuclear data library. It is in evidence that this numerical method can be used in the place of the extra physical approximations.

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Vibrational spectra of light and heavy water with application to neutron cross section calculations

Cited by 25 publications

References 23 publications

Nuclear Quantum Effects from the Analysis of Smoothed Trajectories: Pilot Study for Water

Nuclear Quantum Effects from the Analysis of Smoothed Trajectories: Pilot Study for Water

Isotope Effects in Water: Differences of Structure, Dynamics, Spectrum, and Proton Transport between Heavy and Light Water from ReaxFF Reactive Force Field Simulations

Convolutional discrete Fourier transform method for calculating thermal neutron cross section in liquids

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