Fully Quantum Description of the Zundel Ion: Combining Variational Quantum Monte Carlo with Path Integral Langevin Dynamics

Mouhat, Félix; Sorella, Sandro; Vuilleumier, Rodolphe; Saitta, A. Marco; Casula, Michele

doi:10.1021/acs.jctc.7b00017

Cited by 34 publications

(53 citation statements)

References 114 publications

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“…Once these modes are optimally coupled, one is left with just the classical problem of how to efficiently thermostat the diffusive centroid degrees of freedom. Together these approaches, combined with new integrators to give additional stability [40,41], have alleviated most of the issues that have previously limited time steps and efficiency in path integral simulations.…”

Section: Efficient Integrators and Thermostats For Pimentioning

confidence: 99%

Nuclear quantum effects enter the mainstream

2018

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Over the past decades, atomistic simulations of chemical, biological and materials systems have become increasingly precise and predictive thanks to the development of accurate and efficient techniques that describe the quantum mechanical behavior of electrons. However, the overwhelming majority of such simulations still assume that the nuclei behave as classical particles. While historically this approximation could sometimes be justified due to complexity and computational overhead, the lack of nuclear quantum effects has become one of the biggest sources of error when systems containing light atoms are treated using current state-of-the-art descriptions of chemical interactions. Over the past decade, this realization has spurred a series of methodological advances that have led to dramatic reductions in the cost of including these important physical effects in the structure and dynamics of chemical systems. Here we show how these developments are now allowing nuclear quantum effects to become a mainstream feature of molecular simulations. These advances have led to new insights into chemical processes in the condensed phase and open the door to many exciting future opportunities.The Born Oppenheimer approximation to separate the electronic and nuclear wavefunctions underpins the concept of potential energy surfaces and forms the bedrock of any modern chemistry course. Much less attention, however, is generally given to the routinely assumed additional approximation employed in atomistic simulations that the nuclear motion and sampling on the resulting electronic energy surface can be treated classically. Within the classical nuclei approximation, one loses the ability to describe nuclear zero-point energy, quantization of energy levels, and tunneling, as well as exchange and coherence effects. However, even at room temperature the zero-point energy of a typical chemical bond of frequency ω (∼ ω/2) exceeds the thermal energy scale of that coordinate at temperature T (∼k B T ) by an order of magnitude. These effects can thus make large changes to the structure and dynamics in processes ranging from proton delocalization and tunneling in enzymes [1][2][3][4] to changes in the stability of crystal polymorphs [5] to the the phase diagram of high pressure melts [6]. A revealing consequence of neglecting nuclear quantum effects (NQEs) is that equilibrium isotope effects would be predicted to be zero, despite forming the basis of vital analysis methods in fields ranging from the atmospheric sciences to biochemistry and materials science.In addition to the importance of calculating and understanding these properties, modelling the quantum nature of the nuclei has become increasingly important due to the greater availability of accurate and affordable methods to describe the electronic potential energy surface on which the nuclei evolve. The accuracy of these surfaces is constantly improving, and the most recent generation of state-of-the art potential energy surfaces are now usually generated either by on-the-fly evalu...

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Section: Efficient Integrators and Thermostats For Pimentioning

confidence: 99%

Nuclear quantum effects enter the mainstream

2018

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“…These equations are integrated using the efficient Path-Integrals Ornstein-Uhlenbeck Dynamics (PIOUD) algorithm of ref. 36, that we adapted to the case of an open chain of harmonically coupled beads as explained in the supplementary information. The auxiliary sampling is mainly responsible for the high numerical cost of the method.…”

Section: B Auxiliary Langevin Dynamicsmentioning

confidence: 99%

Sampling the thermal Wigner density via a generalized Langevin dynamics

Plé

Huppert

Finocchi

et al. 2019

The Journal of Chemical Physics

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The Wigner thermal density is a function of considerable interest in the area of approximate (linearized or semiclassical) quantum dynamics where it is employed to generate initial conditions for the propagation of appropriate sets of classical trajectories. In this paper, we propose an original approach to compute the Wigner density, based on a generalized Langevin equation. The stochastic dynamics is non-trivial in that it contains a coordinate-dependent friction coefficient and a generalized force that couples momenta and coordinates. These quantities are, in general, not known analytically and have to be estimated via auxiliary calculations. The performance of the new sampling scheme is tested on standard model systems with highly non classical features such as relevant zero point energy effects, correlation between momenta and coordinates, and negative parts of the Wigner density. In its current brute force implementation, the algorithm, whose convergence can be systematically checked, is accurate and has only limited overhead compared to schemes with similar characteristics. We briefly discuss potential ways to further improve its numerical efficiency.

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“…More broadly, combining path integral methods with higher level methods such as quantum Monte Carlo and quantum chemistry approaches is clearly an exciting avenue for future research [84,206,207]. Indeed, given the recent progress with quantum Monte Carlo approaches in terms of accuracy, efficiency, and the calculation of forces, QMC-based PIMD simulations look like a promising way of treating particularly challenging systems [51,[208][209][210]. Methods for dealing with non-adiabatic effects is another area where excellent progress is being made on topics such as understanding NQEs in electron transfer [211][212][213][214][215][216].…”

Section: A Quantum Delocalisation In Hydrogen Bondsmentioning

confidence: 99%

“…This has included important work on quantum dynamics within the path-integral framework, with e.g. centroid molecular dynamics (CMD) [46][47][48], ringpolymer molecular dynamics (RPMD) [37,49,50], and the combination of path integral methods with other electronic structure methods beyond DFT [51][52][53][54]. Developments have also been made in combining the path integral framework with other quantum theories, for example the instanton theory [55][56][57][58][59].…”

Section: Introductionmentioning

confidence: 99%

The quantum nature of hydrogen

Fang

Chen

Feng

et al. 2019

International Reviews in Physical Chemistry

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Hydrogen is the most abundant element. It is also the most quantum, in the sense that quantum tunnelling, quantum delocalisation, and zero-point motion can be important. For practical reasons most computer simulations of materials have not taken such effects into account, rather they have treated nuclei as classical particles. However, thanks to methodological developments over the last few decades, nuclear quantum effects can now be treated in complex materials. Here we discuss our studies on the role nuclear quantum effects play in hydrogen containing systems. We give examples of how the quantum nature of the nuclei has a significant impact on the location of the boundaries between phases in high pressure condensed hydrogen. We show how nuclear quantum effects facilitate the dissociative adsorption of molecular hydrogen on solid surfaces and the diffusion of atomic hydrogen across surfaces. Finally, we discuss how nuclear quantum effects alter the strength and structure of hydrogen bonds, including those in DNA. Overall these studies demonstrate that nuclear quantum effects can manifest in different, interesting, and non-intuitive ways. Whilst historically it has been difficult to know in advance what influence nuclear quantum effects will have, some of the important conceptual foundations have now started to emerge.

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Fully Quantum Description of the Zundel Ion: Combining Variational Quantum Monte Carlo with Path Integral Langevin Dynamics

Cited by 34 publications

References 114 publications

Nuclear quantum effects enter the mainstream

Nuclear quantum effects enter the mainstream

Sampling the thermal Wigner density via a generalized Langevin dynamics

The quantum nature of hydrogen

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