We studied the positron (e+) interaction with the hydrogen molecular dianion H22− to form the positronic bound state of [H−; e+; H−] using the first-principles quantum Monte Carlo method combined with the multi-component molecular orbital one. H22− itself is unstable, but it was shown that such an unbound H22− may become stable by intermediating a positron and forming the positronic covalent bond of the [H−; e+; H−] system [J. Charry et al., Angew. Chem., Int. Ed. 57, 8859–8864 (2018)]. We newly found that [H−; e+; H−] has double minima containing another positronic bound state of [H2; Ps−]-like configuration with the positronium negative ion Ps− at the bond distance approximately equal to the equilibrium H2 molecule. Our multi-component variational Monte Carlo calculation and the multi-component configuration interaction one resulted in the positronic covalent bonded structure being the global minimum, whereas a more sophisticated multi-component diffusion Monte Carlo calculation clearly showed that the [H2; Ps−]-like structure at the short bond distance is energetically more stable than the positronic covalent bonded one. The relaxation due to interparticle correlation effects pertinent to Ps− (or Ps) formation is crucial for the formation of the Ps−A2-like structure for binding a positron to the non-polar negatively charged dihydrogen.
First-principles quantum Monte Carlo studies for prediction of double minima for positronic hydrogen molecular dianion
Note: This paper is part of the JCP Special Topic on Frontiers of Stochastic Electronic Structure Calculations.
Shumpei Ito, Daisuke Yoshida, Yukiumi Kita, Masanori Tachikawa; First-principles quantum Monte Carlo studies for prediction of double minima for positronic hydrogen molecular dianion. J. Chem. Phys. 14 December 2020; 153 (22): 224305. https://doi.org/10.1063/5.0022673
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