Bergami Mateus, Santana Andre L D, Charry Martinez Jorge, Reyes Andres, Coutinho Kaline, Varella Márcio T do N
Instituto de Física, Universidade de São Paulo, Rua do Matão 1371 CP 66318, CEP 05508-090 São Paulo, SP, Brazil.
Department of Physics and Materials Science, University of Luxembourg, L-1511 Luxembourg City, Luxembourg.
J Phys Chem B. 2022 Apr 14;126(14):2699-2714. doi: 10.1021/acs.jpcb.1c10124. Epub 2022 Apr 4.
We propose a model for solvated positronium (Ps) atoms in water, based on the sequential quantum mechanics/molecular mechanics (s-QM/MM) protocol. We developed a Lennard-Jones force field to account for Ps-water interactions in the MM step. The repulsive term was obtained from a previously reported model for the solvated electron, while the dispersion constant was derived from the Slater-Kirkwood formula. The force field was employed in classical Monte Carlo (MC) simulations to generate Ps-solvent configurations in the ensemble, while the quantum properties were computed with the any-particle molecular orbital method in the subsequent QM step. Our approach is general, as it can be applied to other liquids and materials. One basically needs to describe the solvated electron in the environment of interest to obtain the Ps solvation model. The thermodynamical properties computed from the MC simulations point out similarities between the solvation of Ps and noble gas atoms, hydrophobic solutes that form clathrate structures. We performed convergence tests for the QM step, with particular attention to the choice of basis set and expansion centers for the positronic and electronic subsystems. Our largest model was composed of the Ps atom and 22 water molecules in the QM region, corresponding to the first solvation shell, surrounded by 128 molecules described as point charges. The mean electronic and positronic vertical detachment energies were (4.73 ± 0.04) eV and (5.33 ± 0.04) eV, respectively. The latter estimates were computed with Koopmans' theorem corrected by second-order self-energies, for a set of statistically uncorrelated MC configurations. While the Hartree-Fock wave functions do not properly account for the annihilation rates, they were useful for numerical tests, pointing out that annihilation is more sensitive to the choice of basis sets and expansion centers than the detachment energies. We further explored a model with reduced solute cavity size by changing the Ps-solvent force field. Although the pick-off annihilation lifetimes were affected by the cavity size, essentially the same conclusions were drawn from both models.
我们基于顺序量子力学/分子力学（s-QM/MM）协议，提出了一种用于水中溶剂化正电子素（Ps）原子的模型。我们开发了一种 Lennard-Jones 力场，以在分子力学步骤中考虑 Ps 与水的相互作用。排斥项取自先前报道的溶剂化电子模型，而色散常数则由 Slater-Kirkwood 公式推导得出。该力场用于经典蒙特卡罗（MC）模拟，以在系综中生成 Ps - 溶剂构型，而量子性质则在随后的量子力学步骤中用任意粒子分子轨道方法计算。我们的方法具有通用性，因为它可以应用于其他液体和材料。基本上，为了获得 Ps 溶剂化模型，需要描述感兴趣环境中的溶剂化电子。从 MC 模拟计算出的热力学性质指出了 Ps 溶剂化与稀有气体原子、形成笼形结构的疏水溶质之间的相似性。我们对量子力学步骤进行了收敛测试，特别关注正电子和电子子系统的基组选择和展开中心。我们最大的模型在量子力学区域由 Ps 原子和 22 个水分子组成，对应于第一溶剂化层，周围有 128 个被描述为点电荷的分子。平均电子和正电子垂直脱离能分别为（4.73 ± 0.04）eV 和（5.33 ± 0.04）eV。后者的估计值是用二阶自能校正的 Koopmans 定理，针对一组统计上不相关的 MC 构型计算得出的。虽然 Hartree-Fock 波函数不能正确考虑湮灭率，但它们对数值测试很有用，指出湮灭对基组和展开中心的选择比脱离能更敏感。我们通过改变 Ps - 溶剂力场进一步探索了一个溶质腔尺寸减小的模型。尽管拾取湮灭寿命受腔尺寸影响，但从两个模型得出的基本结论相同。
