Thermal dissociation of dipositronium: Path-integral Monte Carlo approach

Abstract

Path integral Monte Carlo simulation of the dipositronium "molecule" Ps2 reveals its surprising thermal instability. Although, the binding energy is ∼ 0.4 eV, due to the strong temperature dependence of its free energy Ps2 dissociates, or does not form, above ∼ 1000 K, except for high densities where a small fraction of molecules are in equilibrium with Ps atoms. This prediction is consistent with the recently reported first observation of stable Ps2 molecules by Cassidy & Mills Jr., Nature 449, 195 (07), and Phys.Rev.Lett. 100, 013401 (08); at temperatures below 1000 K. The relatively sharp transition from molecular to atomic equilibrium, that we find, remains to be experimentally verified. To shed light on the origin of the large entropy factor in free energy we analyze the nature of interatomic interactions of these strongly correlated quantum particles. The conventional diatomic potential curve is given by the van der Waals interaction at large distances, but due to the correlations and high delocalization of constituent particles the concept of potential curve becomes ambiguous at short atomic distances.

Experimental progress in positronium laser physics

“…A wide variety of theoretical techniques have been used to deal with this system (e.g. [566][567][568][569][570][571][572][573]). Shortly after Wheeler's paper was published [16] the stability of Ps 2 was demonstrated by Hylleraas and Ore, who obtained a binding energy of 0.11 eV using variational methods [507].…”

Finite temperature quantum statistics of H3+ molecular ion

“…[14][15][16][17][18][19][20][21] For 0 K data with benchmark accuracies, however, the conventional quantum chemistry or other Monte Carlo methods, such as the diffusion Monte Carlo, 22 are more appropriate. [14][15][16][17][18][19][20][21] For 0 K data with benchmark accuracies, however, the conventional quantum chemistry or other Monte Carlo methods, such as the diffusion Monte Carlo, 22 are more appropriate.…”

Density-matrix-renormalization-group study of a one-dimensional diatomic molecule beyond the Born-Oppenheimer approximation

“…Such systems are difficult to treat analytically. Various numerical approaches, such as the stochastic variational method (SVM)[7-9], quantum Monte Carlo (QMC) methods [10,11], and Exact Factorization [6,12,13] combined with Density Functional Theory (DFT), have been applied to explore the spectrum of the systems in two or three dimensions and have correctly predicted the bound ground state [3] and possible bound excited states [8,9] later proved by experiments [4].The hydrogen molecule (H 2 ) and the positronium molecule (Ps 2 ) are in nearly opposite limits of mass ratios between the nuclei and electrons, 1836:1 vs 1:1, corresponding to adiabatic and non-adiabatic limits, respectively. Unlike H 2 , for which the BO approximation can be used to simplify the numerical treatments [14], the nonadiabatic features of Ps 2 requires a complete four-body treatment.…”

“…Such systems are difficult to treat analytically. Various numerical approaches, such as the stochastic variational method (SVM) [7][8][9], quantum Monte Carlo (QMC) methods [10,11], and Exact Factorization [6,12,13] combined with Density Functional Theory (DFT), have been applied to explore the spectrum of the systems in two or three dimensions and have correctly predicted the bound ground state [3] and possible bound excited states [8,9] later proved by experiments [4].…”