Calculated properties of the commensurate monolayers of helium and hydrogen on graphite

Gottlieb, Joel M.; Bruch, L. W.

doi:10.1103/physrevb.41.7195

Cited by 34 publications

(11 citation statements)

References 8 publications

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“…Ni and Bruch, 28 using the Hartree-Jastrow approximation and the Lennard-Jones potential, calculated the ground state energy and the nearest-neighbor spacing for monolayer solids of H 2 adsorbed on the basal plane surface of graphite. Gottlieb and Bruch,29,30 using a Jastrow-variational approximation, calculated the energy and the structure of the commensurate and the domain-wall monolayer solids of molecular hydrogen adsorbed on graphite. Novaco 31 calculated the ground state energy and density of states for the ͱ3ϫͱ3 commensurate solid phase of monolayer H 2 adsorbed on graphite using a self-consistent phonon approximation and investigated the effects of anisotropic admolecule-carbon interaction.…”

Section: Introductionmentioning

confidence: 99%

Submonolayer molecular hydrogen on graphite: A path-integral Monte Carlo study

Nho

Manousakis

2002

Phys. Rev. B

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We have used path-integral Monte Carlo ͑PIMC͒ to simulate molecular hydrogen on graphite at submonolayer coverage. First we use a flat substrate and we study the first layer for various values of the coverage up to layer completion. We found that the first layer has a solid-gas coexistence phase at low densities and a triangular solid phase at and above the equilibrium density 0 ϭ0.0705 Å Ϫ2 . We also determine that the first layer promotion coverage is at 0.094 Å Ϫ2 in agreement with experiment. Second we introduce the full H 2 -graphite interaction, i.e., we include the effects of substrate corrugations. In this case we carry our PIMC simulations on a variety of systems at and below the 1/3 coverage. We calculate the energy as a function of coverage, contour plots of the molecule probability distribution, the pair distribution function, the static structure function and the specific heat. When the substrate corrugation part of the interaction is included we find that at 1/3 coverage the system is in a ͱ3ϫͱ3 commensurate solid phase. At coverages below that and at low enough temperature the system exists in solid clusters surrounded by vapor. At coverages below a critical density, defining a tricrical point, as the system is heated up these clusters melt into a uniform fluid phase. We find that below the commensurate density and above the tricritical point, as the clusters are heated up, first they undergo a transition into a phase where the vapor phase disappears and a commensurate phase with vacancies arises. This commensurate solid melts at higher temperature into a uniform fluid phase.

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Section: Introductionmentioning

confidence: 99%

Submonolayer molecular hydrogen on graphite: A path-integral Monte Carlo study

Nho

Manousakis

2002

Phys. Rev. B

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“…This is a general theorem; Hohenberg [40] applied it to fluctuations in Bose liquids, showing that there can be no ODLRO and thus no BEC in any 1D or 2D system. Similar theorems also prevent diagonal long-range order in less than three dimensions for systems with continuous translational symmetry, but the underlying periodic potential breaks translational symmetry [38], permitting long-range crystalline order in this system (just as it permits a classical 2D solid for 4 He adsorbed on graphite [36,37]). However, presence of a periodic external potential does not permit ODLRO.…”

Section: Resultsmentioning

confidence: 87%

“…As the wavelength of the phonons approaches infinity (k → 0), the phonons represent vibration of the entire system back and forth together, resulting in no net change to the interparticle interactions, but moving the particles out of the minima in the potential and thus coming at a finite energy cost in the presence of a lattice potential [36]. This finite gap between the ground state and the longest wavelength phonons has been measured by neutron scattering [37].…”

Section: Resultsmentioning

confidence: 98%

High-temperature supersolid ofHe4in a one-dimensional periodic potential

Olsen

2015

Phys. Rev. A

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The search for robust experimental proof of supersolidity has encountered many complicating factors, such as temperature-dependent changes in the mechanical properties of solid 4 He which mimic the signature of superfluid flow. As a result, the physical existence and true nature of this unique state of matter are still under debate. Here we consider 4 He stabilized by a one-dimensional periodic potential whose lattice spacing is similar to the length scale of the 4 He-4 He interaction. We use the Bogoliubov transformation to calculate the excitation spectrum, finding that when interactions between nearest or next-nearest neighbors are strongly attractive, there is a finite positive gap in energy between the delocalized ground state and the lowest energy excitations, which is significantly larger than the both the lambda temperature and the melting temperature. Not only does this make the system stable against phase separation of particles and vacancies, but it also means that it should be possible to observe a supersolid at a high-enough temperature that superfluidity in bulk liquid 4 He or changes in the mechanical properties of bulk solid 4 He do not obscure it. The properties of experimentally achievable materials which could support this type of supersolid are also discussed.

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“…Crowell model approximates the total adsorption potential by a sum of spherically symmetric admolecule-carbon interactions, with the admolecule-carbon pair interaction being Lennard-Jones LJ (12,6). The parameters for the LJ(12,6) interaction were originally determined through the use of combination rules.…”

Section: Iiadmolecule-graphite Interactionmentioning

confidence: 99%

Phonon spectrum and density of states for commensurate monolayer phases ofH2, HD, andD2
Novaco
¹

1992
Phys. Rev. B
22
0
16
0
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A self-consistent-phonon approximation was used to calculate the ground-state properties and phonon density of states for the &3 X &3 R 30' commensurate phase of monolayer H2, HD, and D2 adsorbed on graphite. The adsorbed molecules were assumed to be in a pure J =0 rotational state, and the wave function for the solid included coordinates both parallel and perpendicular to the surface. The proper inclusion of the surface-normal terms in the wave function was found to have a significant effect on both the phonon spectrum and the ground-state properties. The calculations for the ground-state energy and the phonon spectrum of these solids were done both with and without the inclusion of short-range correlations, these short-range correlations being treated within a version of the T-matrix approximation. The possible effects of various substrate-mediated interactions, anisotropic admolecule-carbon interactions, and finite temperatures were also investigated. The current theoretical results are compared to those of recent inelastic-neutron-scattering experiments and to previous theoretical results for these systems.

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Calculated properties of the commensurate monolayers of helium and hydrogen on graphite

Cited by 34 publications

References 8 publications

Submonolayer molecular hydrogen on graphite: A path-integral Monte Carlo study

Submonolayer molecular hydrogen on graphite: A path-integral Monte Carlo study

High-temperature supersolid ofHe4in a one-dimensional periodic potential

Phonon spectrum and density of states for commensurate monolayer phases ofH2, HD, andD2
Novaco
¹

1992
Phys. Rev. B
22
0
16
0
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Calculated properties of the commensurate monolayers of helium and hydrogen on graphite

Cited by 34 publications

References 8 publications

Submonolayer molecular hydrogen on graphite: A path-integral Monte Carlo study

Submonolayer molecular hydrogen on graphite: A path-integral Monte Carlo study

High-temperature supersolid ofHe4in a one-dimensional periodic potential

Phonon spectrum and density of states for commensurate monolayer phases ofH2, HD, andD2Novaco1 1992Phys. Rev. B220160View full textAdd to dashboardCite

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Phonon spectrum and density of states for commensurate monolayer phases ofH2, HD, andD2
Novaco
¹

1992
Phys. Rev. B
22
0
16
0
View full text Add to dashboard Cite