Quantum Monte Carlo investigation of small He4 clusters with a He3 impurity

Abstract

Structure and energetics of small helium clusters: Quantum simulations using a recent perturbational pair potential Small helium ( 4 He) clusters containing the lighter isotope 3 He are studied by means of quantum Monte Carlo methods. Accurate ground state energies and structural properties are obtained using accurate trial wave functions and the Tang-Tonnies-Yiu ͑TTY͒ helium-helium pair potential. The dimer 4 He-3 He is not bound; as well as the trimer 4 He 3 He 2 . The smallest cluster containing 3 He is 4 He 2 3 He with a nonrigid structure having a marked linear contribution. Interestingly, this weakly bound system, with an energy one order of magnitude less than the 4 He 3 trimer, is able to bind another 3 He atom, forming the tetramer 4 He 2 3 He 2 , which shows the odd feature of having five out of six unbound pairs. In general, the substitution of a single 4 He atom in a pure cluster with a 3 He atom leads to an energetic destabilization, as the pair 4 He-3 He is not bound. The isotopic impurity is found to perturb only weakly the distributions of the remaining 4 He atoms, which retain the high floppiness already found in the pure clusters. As the number of atoms increases the isotopic impurity has the marked tendency to stay on the surface of the cluster. This behavior is consistent with the formation of the so-called ''Andreev states'' of a single 3 He in liquid 4 He helium and droplets, where the impurity tends to form single-particle states on the surface of the pure 4 He.

Vibrations of closed-shell Lennard-Jones icosahedral and cuboctahedral clusters and their effect on the cluster ground-state energy

“…Thus, even at zero temperature, the thermodynamical equilibrium state of the cluster need not be the same as the state which minimizes the classical potential energy of the cluster [12]. This of course depends on the nature of particles in the system, their mass in particular as is known from the studies of systems of He atoms [22].…”

Predicting atomic dopant solvation in helium clusters: The MgHen case

“…In systems where accurate interaction potentials between helium and the impurity are available, the quantum Monte Carlo (QMC) approach is probably the best suited, and has been already applied successfully to the study of doped helium clusters [6,7,8,9,10,11,12]. Though the DMC simulations cannot recover the temporal evolution of the system, they provide many important quantities that are hardly accessible experimentally, such as radial and angular distribution functions, solvation energies, excitation spectra, as well as their dependence on the size of the helium aggregate.…”

Multipole response of doped He3 drops

“…The main experimental effort has focused on the study of pure and doped 4 He N drops, for which a microscopic description of the ground state (gs) using Monte Carlo techniques 3,[9][10][11][12][13][14][15] , and of the elementary excitations using an optimized variational method 16,17 are available. Density functional calculations of the gs and excitation spectrum using finite-range (FRDF) or zero-range density functionals have been carried out, see Refs.…”