<i>Ab initio</i>two-body potentials and the properties of condensed phases of helium atoms

Ujevic, Sebastian; Vitiello, S. A.

doi:10.1103/physrevb.71.224518

Cited by 13 publications

(12 citation statements)

References 34 publications

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“…It is worthwhile to obtain an equation of state ͑EOS͒ for the solid phase at an accuracy level comparable to the one determined at the liquid phase. Interatomic potentials that in quantum Monte Carlo calculations 16 in the liquid phase give results in excellent agreement with experiment were not able to perform equally well in the solid phase.…”

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confidence: 93%

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Interatomic potential for the condensed phases of helium atoms

Ujevic

Vitiello

2006

Phys. Rev. B

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Results from diffusion Monte Carlo have been used in fits of a damping function of the triple dipole and of the intensity of the exchange three-body interactions. The equations of state obtained considering this threebody potential are in excellent agreement with experiment both at the solid and liquid phases. The calculations show that exchange nonadditivities that contribute less than 0.2% of the two-body potential energy in the solid phase are needed to describe the properties of a system of helium atoms.

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confidence: 93%

“…The calculations were performed with a multiweight DMC method. 13,16 This extension of the standard method allows the determination of the three-body contributions to the total energy to be estimated in a correlated form with the twobody energy. They were obtained without extrapolations and the results are subject only to statistical uncertainties.…”

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confidence: 99%

Interatomic potential for the condensed phases of helium atoms

Ujevic

Vitiello

2006

Phys. Rev. B

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“…[6,7] It is worth mentioning that the interacting potential for the helium atoms is very accurately known as more than one study has shown. [8,9] These facts, together with Monte Carlo calculations performed with a reasonable number of atoms, assure that the estimated quantities can have good reliability.…”

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confidence: 82%

Elastic constants and supersolidity in solid hcp 4He

Pessoa¹,

Koning²,

Vitiello³

2012

Preprint

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The elastic constants of solid hcp 4 He are investigated in molar volumes ranging from about melting up to approximately 14 MPa. Properties of interest are determined by averages formed from computed values in configurations sampled by Monte Carlo of a model wave function. Deviations from known elastic relations are reported near the density where the supersolid fraction is maximum. The results offer further evidence that the supersolid state is related to elastic constants anomalies and that both are manifestations of a single physical process.1 For more than a hundred years, since it has been liquefied, helium has shown intriguing behaviors and has provided invaluable clues for the condensed matter physics. Nowadays, despite a reasonable good understanding of its liquid phase, solid helium is still revealing fascinating aspects that defy experimentalists and theoreticians. The shear modulus softening with temperature increase, as observed by Day and Beamish[1], and its connections to supersolidity, superfluidity superimposed to crystalline order, as seen in the pioneering experiments by Kim and Chan[2, 3] illustrate very well this situation.Elasticity is ubiquitous among materials and has been extensively investigated in solids where atomic exchange is negligible, and the atoms are reasonable localized and distinguishable. If forces that are not too strong are applied in the surfaces of these solids, they will produce mechanical deformations that will increase the potential energy. As the solid is released from these forces and assuming they are small enough, it will go back to its original state. However, what can be said about quantum solids? Systems where the zero-point kinetic energy is comparable to the binding energy of the atoms that perform large excursions from their mean positions in the lattice. How will these quantum systems respond to applied forces?This letter reports values of all the five independent elastic constants, as a function of the density, which characterize a defect-free single crystal of 4 He in an hcp structure. We have analyzed our results using relations among the elastic constants that are satisfied under well defined conditions. Since all the elastic constants were determined, it was possible to some extent verify the internal consistence of our calculations and search for elastic anomalies in this quantum solid. In fact, we have observed deviations of the relations occurring near the same density where the mass decoupling in the movement of torsional oscillators has its maximum. [4] In our view these results are further evidences that supesolidity[2, 3] and elastic anomalies [1,5] of the shear modulus are related phenomena and consequence of a single physical process.The elastic constants were calculated at zero temperature using a model wave function that has allowed an excellent description of various properties of 4 He in both the liquid and solid phases. [6,7] It is worth mentioning that the interacting potential for the helium atoms is very accurately known as more than one...

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“…37) of the walkers have one or two of their weights equal to zero. Certainly this fraction also depends on the potential amplitude λ in the Hamiltonians H (λ).…”

Section: Methodsmentioning

confidence: 99%

Efficient implementation of the Hellmann–Feynman theorem in a diffusion Monte Carlo calculation

Vitiello

2011

The Journal of Chemical Physics

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Kinetic and potential energies of systems of (4)He atoms in the solid phase are computed at T = 0. Results at two densities of the liquid phase are presented as well. Calculations are performed by the multiweight extension to the diffusion Monte Carlo method that allows the application of the Hellmann-Feynman theorem in a robust and efficient way. This is a general method that can be applied in other situations of interest as well.

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Ab initiotwo-body potentials and the properties of condensed phases of helium atoms

Cited by 13 publications

References 34 publications

Interatomic potential for the condensed phases of helium atoms

Interatomic potential for the condensed phases of helium atoms

Elastic constants and supersolidity in solid hcp 4He

Efficient implementation of the Hellmann–Feynman theorem in a diffusion Monte Carlo calculation

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