Abstract
The ground-state phase diagrams of 4 He adsorbed on graphene and graphite are calculated using quantum simulation methods. In this work, a systematic investigation of the approximations used in such simulations is carried out. Particular focus is placed on the helium–helium (He–He) and helium–carbon (He–C) interactions, as well as their modern approximations. On careful consideration of other approximations and convergence, the simulations are otherwise (numerically) exact. The He–He interaction as approximated by a sum of pairwise potentials is quantitatively assessed. A similar analysis is made for the He–C interaction, but more thoroughly and with a focus on surface corrugation. The importance of many-body effects is discussed. Altogether, the results provide “reference data” for the considered systems. Using comparisons with experiments and first-principle calculations, conclusions are drawn regarding the quantitative accuracy of these modern approximations to these interactions.
Highlights
Quantum fluids and solids (QFS) are characterized by particles that interact through weak long-range forces, and for which their quantum kinetic energy Ek is much larger than kB T where kB is the Boltzmann constant and T is the temperature
The ground-state phase diagrams of 4 He adsorbed on graphene and graphite were calculated using quantum simulation methods
The focus is on the phase diagram of 4 He adsorbed on graphene—in particular, for monolayer coverages up to and just above the density of the C1/3 phase at σs ≈ 0.0636 Å−2
Summary
Quantum fluids and solids (QFS) are characterized by particles that interact through weak long-range forces, and for which their quantum kinetic energy Ek is much larger than kB T where kB is the Boltzmann constant and T is the temperature. For the solid phase [1], the quantum motion can lead to spatial fluctuations about the equilibrium lattice sites that are much larger than in any classical solid. These phases are important for several reasons, as they are key to the fundamental understanding of nature, technological applications, and applied interests of many scientific fields. Archetypical examples include hydrogen and helium, which are present in a wide range of thermodynamic conditions [2] One such system that is the subject of many experimental and theoretical studies is the adsorption of helium on a carbon (often graphene or graphite) substrate.
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