The size distributions of neutral 4He clusters in cryogenic jet beams, analyzed by diffraction from a 100 nm period transmission grating, reveal magic numbers at N=10-11, 14, 22, 26-27, and 44 atoms. Whereas magic numbers in nuclei and clusters are attributed to enhanced stabilities, this is not expected for quantum fluid He clusters on the basis of numerous calculations. These magic numbers occur at threshold sizes for which the quantized excitations calculated with the diffusion Monte Carlo method are stabilized, thereby providing the first experimental confirmation for the energy levels of 4He clusters.The size distributions of neutral 4He clusters in cryogenic jet beams, analyzed by diffraction from a 100 nm period transmission grating, reveal magic numbers at N=10-11, 14, 22, 26-27, and 44 atoms. Whereas magic numbers in nuclei and clusters are attributed to enhanced stabilities, this is not expected for quantum fluid He clusters on the basis of numerous calculations. These magic numbers occur at threshold sizes for which the quantized excitations calculated with the diffusion Monte Carlo method are stabilized, thereby providing the first experimental confirmation for the energy levels of 4He clusters.

Physical Review LettersMay 6, 200465 citations

Study of helium droplets using quantum Monte Carlo techniques

E. Sola

Helium systems at zero temperature are strongly correlated neutral systems which can only be described by means of quantum mechanics. The existence of the two isotopes 4He and 3He allows the comparison between the quantum effects due to different statistics, bosonic and fermionic. In this Thesis, an analysis of Helium droplets has been done. Throughout this work, both energetic and structural properties of systems with different number of particles N are obtained by means of the Quantum Monte Carlo techniques (Variational and Diffusion Monte Carlo - VMC and DMC-). Several studies on Helium droplets have been published in the last years, most of them using the mean field theory (as the Density Functional) and variational approaches (as VMC). In the case of 4He, also exact DMC results have already been reported, actually, a great number of works have described with high accuracy the ground state of this bosonic system. The appearance of magic numbers from experimental point of view has motivated the study of 4He droplets, and one chapter of this Thesis is focused on this bosonic system. We have carried out a one-by-one energetic study in the range from 20 to 30 particles using the DMC technique to discuss the existence of magic numbers. On the other hand, a brief study about vortices is also done; using out code, one can calculate the energy of a droplet with one vortex inside (EV) and, therefore, the energy of a vortex (EV -E0). About 3He droplets, the sign problem makes their study quite more difficult, for this reason, the number of works is considerably smaller than in the bosonic case. One aim of this thesis was to write a DMC code using both Fixed and Released Node approximations (FN and RN) able to perform high accurate calculations of energetic and structural properties of these finite fermionic systems.Helium systems at zero temperature are strongly correlated neutral systems which can only be described by means of quantum mechanics. The existence of the two isotopes 4He and 3He allows the comparison between the quantum effects due to different statistics, bosonic and fermionic. In this Thesis, an analysis of Helium droplets has been done. Throughout this work, both energetic and structural properties of systems with different number of particles N are obtained by means of the Quantum Monte Carlo techniques (Variational and Diffusion Monte Carlo - VMC and DMC-). Several studies on Helium droplets have been published in the last years, most of them using the mean field theory (as the Density Functional) and variational approaches (as VMC). In the case of 4He, also exact DMC results have already been reported, actually, a great number of works have described with high accuracy the ground state of this bosonic system. The appearance of magic numbers from experimental point of view has motivated the study of 4He droplets, and one chapter of this Thesis is focused on this bosonic system. We have carried out a one-by-one energetic study in the range from 20 to 30 particles using the DMC technique to discuss the existence of magic numbers. On the other hand, a brief study about vortices is also done; using out code, one can calculate the energy of a droplet with one vortex inside (EV) and, therefore, the energy of a vortex (EV -E0). About 3He droplets, the sign problem makes their study quite more difficult, for this reason, the number of works is considerably smaller than in the bosonic case. One aim of this thesis was to write a DMC code using both Fixed and Released Node approximations (FN and RN) able to perform high accurate calculations of energetic and structural properties of these finite fermionic systems.

Jan 1, 20060 citations

Variational Monte Carlo studies of atoms

Håvard Sandsdalen

Jan 1, 20102 citations

Quantum Monte Carlo Studies of Small Clusters

Gayanath Fernando, James H. Davenport, ARMEN N. KOCHARIAN

APSMar 1, 20040 citations

Stability of Small Mixed Clusters of H4e and H3e Atoms

R. Guardiola, Jesús Navarro

The existence of small helium clusters containing a variable number of $^{\mathrm{4}}\mathrm{H}\mathrm{e}$ and $^{\mathrm{3}}\mathrm{H}\mathrm{e}$ atoms is studied within a variational Monte Carlo calculation employing the Aziz HFD-B(HE) pair interaction. The clusters ${^{\mathrm{4}}\mathrm{H}\mathrm{e}}_{2}$ support one and two $^{\mathrm{3}}\mathrm{H}\mathrm{e}$ atoms; however, the system with three $^{\mathrm{3}}\mathrm{H}\mathrm{e}$ atoms is metastable, and the next bound system requires at least 18 fermions. All clusters obtained by adding $^{\mathrm{3}}\mathrm{H}\mathrm{e}$ atoms to the trimer ${^{\mathrm{4}}\mathrm{H}\mathrm{e}}_{3}$ and the tetramer ${^{\mathrm{4}}\mathrm{H}\mathrm{e}}_{4}$ are bound, but the clusters ${^{\mathrm{4}}\mathrm{H}\mathrm{e}}_{3}$ - ${^{\mathrm{3}}\mathrm{H}\mathrm{e}}_{3,4,5}$ and ${^{\mathrm{4}}\mathrm{H}\mathrm{e}}_{3,4}$ - ${^{\mathrm{3}}\mathrm{H}\mathrm{e}}_{9}$ are metastable. All remaining clusters with three or more bosons and any number of fermions are stable.The existence of small helium clusters containing a variable number of $^{\mathrm{4}}\mathrm{H}\mathrm{e}$ and $^{\mathrm{3}}\mathrm{H}\mathrm{e}$ atoms is studied within a variational Monte Carlo calculation employing the Aziz HFD-B(HE) pair interaction. The clusters ${^{\mathrm{4}}\mathrm{H}\mathrm{e}}_{2}$ support one and two $^{\mathrm{3}}\mathrm{H}\mathrm{e}$ atoms; however, the system with three $^{\mathrm{3}}\mathrm{H}\mathrm{e}$ atoms is metastable, and the next bound system requires at least 18 fermions. All clusters obtained by adding $^{\mathrm{3}}\mathrm{H}\mathrm{e}$ atoms to the trimer ${^{\mathrm{4}}\mathrm{H}\mathrm{e}}_{3}$ and the tetramer ${^{\mathrm{4}}\mathrm{H}\mathrm{e}}_{4}$ are bound, but the clusters ${^{\mathrm{4}}\mathrm{H}\mathrm{e}}_{3}$-${^{\mathrm{3}}\mathrm{H}\mathrm{e}}_{3,4,5}$ and ${^{\mathrm{4}}\mathrm{H}\mathrm{e}}_{3,4}$-${^{\mathrm{3}}\mathrm{H}\mathrm{e}}_{9}$ are metastable. All remaining clusters with three or more bosons and any number of fermions are stable.

Physical Review LettersOct 17, 200217 citations

The existence of small helium clusters containing a variable number of

^{\mathrm{4}}\mathrm{H}\mathrm{e}

and

^{\mathrm{3}}\mathrm{H}\mathrm{e}

atoms is studied within a variational Monte Carlo calculation employing the Aziz HFD-B(HE) pair interaction. The clusters

{^{\mathrm{4}}\mathrm{H}\mathrm{e}}_{2}

support one and two

^{\mathrm{3}}\mathrm{H}\mathrm{e}

atoms; however, the system with three

^{\mathrm{3}}\mathrm{H}\mathrm{e}

atoms is metastable, and the next bound system requires at least 18 fermions. All clusters obtained by adding

^{\mathrm{3}}\mathrm{H}\mathrm{e}

atoms to the trimer

{^{\mathrm{4}}\mathrm{H}\mathrm{e}}_{3}

and the tetramer

{^{\mathrm{4}}\mathrm{H}\mathrm{e}}_{4}

are bound, but the clusters

{^{\mathrm{4}}\mathrm{H}\mathrm{e}}_{3}

{^{\mathrm{3}}\mathrm{H}\mathrm{e}}_{3,4,5}

and

{^{\mathrm{4}}\mathrm{H}\mathrm{e}}_{3,4}

{^{\mathrm{3}}\mathrm{H}\mathrm{e}}_{9}

are metastable. All remaining clusters with three or more bosons and any number of fermions are stable.