Zero-Point Energy Leakage in Quantum Thermal Bath Molecular Dynamics Simulations

Brieuc, Fabien; Bronstein, Yael; Dammak, Hichem; Depondt, Philippe; Finocchi, Fabio; Hayoun, Marc

doi:10.1021/acs.jctc.6b00684

Cited by 43 publications

(79 citation statements)

References 40 publications

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“…The quantum heat bath technique is an approximate method to capture the quantum lattice vibrations of solids, which cannot treat systems with pathologically strong anharmonicity [34][35][36] as zero-point energy is erroneously distributed between all the vibrational modes. However, when parametrised with care, the method is in principle able to treat realistic potentials [24,37], providing the heat bath friction constant is sufficiently high to prevent zero-point energy leakage but sufficiently weak to allow correct anharmonic behaviour. Whilst this is not in general possible for all systems [37], the strength of atomic bonding in tungsten allows this to be achieved with a parametrisation similar to that used in previous studies [24] (see supplementary material).…”

Section: Quantum Heat Bath Molecular Dynamicsmentioning

confidence: 99%

“…However, when parametrised with care, the method is in principle able to treat realistic potentials [24,37], providing the heat bath friction constant is sufficiently high to prevent zero-point energy leakage but sufficiently weak to allow correct anharmonic behaviour. Whilst this is not in general possible for all systems [37], the strength of atomic bonding in tungsten allows this to be achieved with a parametrisation similar to that used in previous studies [24] (see supplementary material).…”

Section: Quantum Heat Bath Molecular Dynamicsmentioning

confidence: 99%

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Low temperature diffusivity of self-interstitial defects in tungsten

Swinburne

Dudarev

2017

New J. Phys.

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The low temperature diffusivity of nanoscale crystal defects, where quantum mechanical fluctuations are known to play a crucial role, are essential to interpret observations of irradiated microstructures conducted at cryogenic temperatures. Using density functional theory calculations, quantum heat bath molecular dynamics and open quantum systems theory, we evaluate the low temperature diffusivity of self-interstitial atom clusters in tungsten valid down to temperatures of 1 K. Due to an exceptionally low defect migration barrier, our results show that interstitial defects exhibit very high diffusivity of order m -10 m s 3 2 1 over the entire range of temperatures investigated.

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Section: Quantum Heat Bath Molecular Dynamicsmentioning

confidence: 99%

Section: Quantum Heat Bath Molecular Dynamicsmentioning

confidence: 99%

Low temperature diffusivity of self-interstitial defects in tungsten

Swinburne

Dudarev

2017

New J. Phys.

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“…The disadvantage of both methods (PIMD and QTB-PIMD) is that time correlation functions are not directly accessible. The sequence of phase transitions in BTO has been successfully retrieved by QTB-MD with a high value of [19] and by QTB-PIMD [7]. In contrast, the values of the ferroelectric polarization in BTO close to the temperatures of the phase-transitions are better computed in QTB-PIMD.…”

Section: Discussionmentioning

confidence: 99%

“…where is the frictional coefficient. The equation of motion is thus: In contrast to the Langevin thermostat, is ω-dependent and the random force components are generated using the procedure detailed in References [18] and [19]. In summary, for MD time steps, , the random force, ̃, is first generated in the Fourier space ( = 2 ): where and are normally distributed random numbers, and i the imaginary number.…”

Section: Quantum Thermal Bath Molecular Dynamics (Qtb-md)mentioning

confidence: 99%

Nuclear quantum effects in molecular dynamics simulations

Dammak

Hayoun

Brieuc

et al. 2018

J. Phys.: Conf. Ser.

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To take into account nuclear quantum effects on the dynamics of atoms, the path integral molecular dynamics (PIMD) method used since 1980s is based on the formalism developed by R. P. Feynman. However, the huge computation time required for the PIMD reduces its range of applicability. Another drawback is the requirement of additional techniques to access time correlation functions (ring polymer MD or centroid MD). We developed an alternative technique based on a quantum thermal bath (QTB) which reduces the computation time by a factor of ~20. The QTB approach consists in a classical Langevin dynamics in which the white noise random force is replaced by a Gaussian random force having the power spectral density given by the quantum fluctuation-dissipation theorem. The method has yielded satisfactory results for weakly anharmonic systems: the quantum harmonic oscillator, the heat capacity of a MgO crystal, and isotope effects in 7 LiH and 7 LiD. Unfortunately, the QTB is subject to the problem of zero-point energy leakage (ZPEL) in highly anharmonic systems, which is inherent in the use of classical mechanics. Indeed, a part of the energy of the highfrequency modes is transferred to the low-frequency modes leading to a wrong energy distribution. We have shown that in order to reduce or even eliminate ZPEL, it is sufficient to increase the value of the frictional coefficient. Another way to solve the ZPEL problem is to combine the QTB and PIMD techniques. It requires the modification of the power spectral density of the random force within the QTB. This combination can also be seen as a way to speed up the PIMD.

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“…In other words, Eqs. (45)(46)(47)(48)(49)(50) should recover the true FGR rate of the excited state decay by correcting Ehrenfest dynamics.…”

Section: Liouville Equationmentioning

confidence: 99%

Ehrenfest+R dynamics. I. A mixed quantum–classical electrodynamics simulation of spontaneous emission

Chen

Sukharev

et al. 2019

The Journal of Chemical Physics

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The dynamics of an electronic system interacting with an electromagnetic field is investigated within mixed quantum-classical theory. Beyond the classical path approximation (where we ignore all feedback from the electronic system on the photon field), we consider all electron-photon interactions explicitly according to Ehrenfest (i.e. mean-field) dynamics and a set of coupled Maxwell-Liouville equations. Because Ehrenfest dynamics cannot capture certain quantum features of the photon field correctly, we propose a new Ehrenfest+R method that can recover (by construction) spontaneous emission while also distinguishing between electromagnetic fluctuations and coherent emission.

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Zero-Point Energy Leakage in Quantum Thermal Bath Molecular Dynamics Simulations

Cited by 43 publications

References 40 publications

Low temperature diffusivity of self-interstitial defects in tungsten

Low temperature diffusivity of self-interstitial defects in tungsten

Nuclear quantum effects in molecular dynamics simulations

Ehrenfest+R dynamics. I. A mixed quantum–classical electrodynamics simulation of spontaneous emission

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