Predicting atomic dopant solvation in helium clusters: The MgHen case

Abstract

We present a quantum Monte Carlo study of the solvation and spectroscopic properties of the Mg doped helium clusters MgHen with n = 2 − 50. Three high level (MP4, CCSD(T) and CCSDT) MgHe interaction potentials have been used to study the sensitivity of the dopant location on the shape of the pair interaction. Despite the similar MgHe well depth, the pair distribution functions obtained in the diffusion Monte Carlo simulations markedly differ for the three pair potentials, therefore indicating different solubility properties for Mg in Hen. Moreover, we found interesting size effects for the behavior of the Mg impurity.As a sensitive probe of the solvation properties, the Mg excitation spectra have been simulated for various cluster sizes and compared with the available experimental results. The interaction between the excited 1 P Mg atom and the He moiety has been approximated using the Diatomics-in-Molecules method and the two excited 1 Π and 1 Σ MgHe potentials. The shape of the simulated MgHe50 spectra show a substantial dependency on the location of the Mg impurity, and hence on the MgHe pair interaction employed.To unravel the dependency of the solvation behavior on the shape of the computed potentials, exact Density Functional Theory has been adapted to the case of doped Hen and various energy distributions have been computed. The results indicate the shape of the repulsive part of the MgHe potential as an important cause of the different behaviours.

Mg impurity in helium droplets

“…The typical distance between the impurity and the center-of-mass of the droplet decreases as the impurity becomes fully solvated. Our results thus confirm those of Mella et al 14 Finally, we have employed the pure estimator to determine the radial structure for the isotopically pure N 4 = 8 and 30 droplets. We have found that the differences between pure and mixed estimators of the radial densities are very small and not worth to be plotted.…”

“…Within Density Functional Theory (DFT), it has been found to solvate in 3 He droplets and to be very delocalized in 4 He ones. 10,13 Previous diffusion Monte Carlo calculations (DMC) 14 have yielded the result that Mg is fully solvated for a critical number of 4 He atoms of about N 4 = 30. A similar transition from surface to bulk location of Mg was also found within DFT.…”

The thermodynamic and ground state properties of the TIP4P water octamer

“…Clearly, variational ͑VMC͒ and DMC are much simpler in flat manifolds. [87][88][89][90][91][92][93][94][95][96][97][98][99][100][101][102] The works we have cited are applications of VMC and DMC to clusters in Cartesian coordinates, and constitute only a small sample of the most recent investigations. On the other hand, diffusion in manifolds remains a topic of research in pure mathematics as well as mathematical physics.…”

Ca impurity in small mixed H4e–H3e clusters

“…In spite of this bulk location, the Ca@ 3 He 40 cluster is not spherically symmetric. This also happens for clusters doped with other weakly attractive impurities, such as Mg in small 4 He clusters [38]. The reason is the tendency of the system to have a helium density as close as possible to its liquid value in order to maximize its binding.…”

“…than can be interpreted as the negative of the He evaporation energies [38]. We have plotted −∆(N 3 ) in Fig.…”