In this thesis I present studies of a number of quantum many-body Bose systems via Quantum Monte Carlo methods. We investigated the dynamic structure factor of a hard-sphere Bose system simulated at T=0 at different densities, from the dilute to the strongly interacting regimes. By increasing the density we observed the spectrum evolves from the weakly interacting Bogoliubov to a phonon-maxon-roton dispersion, but also the emergence of a broad multi-quasiparticle component. For a system with sphere radius and density corresponding to superfluid 4He at equilibrium, we found good agreement with the spectrum in the roton region. In another work, a liquid of distinguishable 4He atoms near freezing at T=1 K was studied to compute the equation of state and static density response function. The results of this study have been used to improve the description of the superfluid-to-solid transition within the Density Functional Theory. Measurements of crystallization kinetics in supercooled liquid p-H2--o-D2 mixtures showed a slowdown with respect to the pure counterparts. In order to contribute to the interpretation of these results we simulated these metastable mixtures. We found differences in the quantum delocalization of the two isotopic molecules, which result in different effective sizes. We characterized also the differences in the local order around the molecules of each species. These results revealed that the observed slowdown is due to purely quantum effects. Finally, in a QMC study of ion Ar+ doped 4He nanodroplets at T=1 K, we computed density profiles, energies, and investigated local order around the Ar+ ion. We found stable solid structures around the ion composed of three solvation shells having the shape of platonic solids: an icosahedron, a dodecahedron, and, again, an icosahedron, with 12, 20, and 12 4He atoms, going from the inner to the outer shell respectively. These results confirmed the interpretation of experimental measurements of the abundances of Ar+@4He nanodroplets.

MICROSCOPIC STUDIES OF STATIC AND DYNAMIC PROPERTIES IN QUANTUM LIQUIDS AND GASES / F. Tramonto ; tutor: D. E. Galli ; coordinatore: M. R. F. Bersanelli. - : . DIPARTIMENTO DI FISICA, 2015 Jan 27. ((27. ciclo, Anno Accademico 2014. [10.13130/tramonto-filippo_phd2015-01-27].

MICROSCOPIC STUDIES OF STATIC AND DYNAMIC PROPERTIES IN QUANTUM LIQUIDS AND GASES

F. Tramonto
2015-01-27

Abstract

In this thesis I present studies of a number of quantum many-body Bose systems via Quantum Monte Carlo methods. We investigated the dynamic structure factor of a hard-sphere Bose system simulated at T=0 at different densities, from the dilute to the strongly interacting regimes. By increasing the density we observed the spectrum evolves from the weakly interacting Bogoliubov to a phonon-maxon-roton dispersion, but also the emergence of a broad multi-quasiparticle component. For a system with sphere radius and density corresponding to superfluid 4He at equilibrium, we found good agreement with the spectrum in the roton region. In another work, a liquid of distinguishable 4He atoms near freezing at T=1 K was studied to compute the equation of state and static density response function. The results of this study have been used to improve the description of the superfluid-to-solid transition within the Density Functional Theory. Measurements of crystallization kinetics in supercooled liquid p-H2--o-D2 mixtures showed a slowdown with respect to the pure counterparts. In order to contribute to the interpretation of these results we simulated these metastable mixtures. We found differences in the quantum delocalization of the two isotopic molecules, which result in different effective sizes. We characterized also the differences in the local order around the molecules of each species. These results revealed that the observed slowdown is due to purely quantum effects. Finally, in a QMC study of ion Ar+ doped 4He nanodroplets at T=1 K, we computed density profiles, energies, and investigated local order around the Ar+ ion. We found stable solid structures around the ion composed of three solvation shells having the shape of platonic solids: an icosahedron, a dodecahedron, and, again, an icosahedron, with 12, 20, and 12 4He atoms, going from the inner to the outer shell respectively. These results confirmed the interpretation of experimental measurements of the abundances of Ar+@4He nanodroplets.
GALLI, DAVIDE EMILIO
BERSANELLI, MARCO RINALDO FEDELE
excited states; collective modes; rotons; phonons; maxons; dynamic structure factor; static structure factor; static density response function; bosons; hard spheres; 4He; helium; superfluidity; superfluid 4He; quantum liquid; quantum solid; quantum gas; Bose statistics; quantum Monte Carlo; path integral Monte Carlo; path integral ground state; 4He nanodroplets; argon; argon ion; cation; supercooled liquid; crystallization; para-hydrogen; ortho-deuterium; binary mixtures; solvation shells; icosahedron; dodecahedron
Settore FIS/03 - Fisica della Materia
MICROSCOPIC STUDIES OF STATIC AND DYNAMIC PROPERTIES IN QUANTUM LIQUIDS AND GASES / F. Tramonto ; tutor: D. E. Galli ; coordinatore: M. R. F. Bersanelli. - : . DIPARTIMENTO DI FISICA, 2015 Jan 27. ((27. ciclo, Anno Accademico 2014. [10.13130/tramonto-filippo_phd2015-01-27].
Doctoral Thesis
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/2434/260418
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