Cassidy J P, Hofierka J, Cunningham B, Green D G
Centre for Light-Matter Interactions, School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, Northern Ireland, United Kingdom.
J Chem Phys. 2024 Feb 28;160(8). doi: 10.1063/5.0188719.
The energetic stability of positron-dianion systems [A-; e+; A-] is studied via many-body theory, where A- includes H-, F-, Cl-, and the molecular anions (CN)- and (NCO)-. Specifically, the energy of the system as a function of ionic separation is determined by solving the Dyson equation for the positron in the field of the two anions using a positron-anion self-energy as constructed in Hofierka et al. [Nature 606, 688 (2022)] that accounts for correlations, including polarization, screening, and virtual-positronium formation. Calculations are performed for a positron interacting with H22-, F22-, and Cl22- and are found to be in good agreement with previous theory. In particular, we confirm the presence of two minima in the potential energy of the [H-; e+; H-] system with respect to ionic separation: a positronically bonded [H-; e+; H-] local minimum at ionic separations r ∼ 3.4 Å and a global minimum at smaller ionic separations r ≲ 1.6 Å that gives overall instability of the system with respect to dissociation into a H2 molecule and a positronium negative ion, Ps-. The first predictions are made for positronic bonding in dianions consisting of molecular anionic fragments, specifically for (CN)22- and (NCO)22-. In all cases, we find that the molecules formed by the creation of a positronic bond are stable relative to dissociation into A- and e+A- (positron bound to a single anion), with bond energies on the order of 1 eV and bond lengths on the order of several ångstroms.
通过多体理论研究了正电子双负离子体系[A⁻; e⁺; A⁻]的能量稳定性，其中A⁻包括H⁻、F⁻、Cl⁻以及分子阴离子(CN)⁻和(NCO)⁻。具体而言，利用霍菲尔卡等人[《自然》606, 688 (2022)]构建的考虑了包括极化、屏蔽和虚正电子素形成等相关性的正电子 - 阴离子自能，通过求解正电子在两个阴离子场中的戴森方程，确定了体系能量随离子间距的变化关系。对正电子与H₂²⁻、F₂²⁻和Cl₂²⁻相互作用进行了计算，结果与先前理论吻合良好。特别地，我们证实了[H⁻; e⁺; H⁻]体系势能随离子间距存在两个极小值：在离子间距r ∼ 3.4 Å处存在一个正电子键合的[H⁻; e⁺; H⁻]局部极小值，在较小离子间距r ≲ 1.6 Å处存在一个全局极小值，这使得体系相对于解离成一个H₂分子和一个正电子素负离子Ps⁻而言整体不稳定。首次对由分子阴离子碎片组成的双负离子中的正电子键合进行了预测，具体针对(CN)₂²⁻和(NCO)₂²⁻。在所有情况下，我们发现通过形成正电子键而形成的分子相对于解离成A⁻和e⁺A⁻（正电子束缚于单个阴离子）是稳定的，键能约为1 eV，键长约为几埃。
