Zen Andrea, Trout Bernhardt L, Guidoni Leonardo
Dipartimento di Fisica, La Sapienza - Università di Roma, Piazzale Aldo Moro 2, 00185 Rome, Italy.
Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, Massachusetts 02139, USA.
J Chem Phys. 2014 Jul 7;141(1):014305. doi: 10.1063/1.4885144.
The electronic properties of the oxygen molecule, in its singlet and triplet states, and of many small oxygen-containing radicals and anions have important roles in different fields of chemistry, biology, and atmospheric science. Nevertheless, the electronic structure of such species is a challenge for ab initio computational approaches because of the difficulties to correctly describe the statical and dynamical correlation effects in presence of one or more unpaired electrons. Only the highest-level quantum chemical approaches can yield reliable characterizations of their molecular properties, such as binding energies, equilibrium structures, molecular vibrations, charge distribution, and polarizabilities. In this work we use the variational Monte Carlo (VMC) and the lattice regularized Monte Carlo (LRDMC) methods to investigate the equilibrium geometries and molecular properties of oxygen and oxygen reactive species. Quantum Monte Carlo methods are used in combination with the Jastrow Antisymmetrized Geminal Power (JAGP) wave function ansatz, which has been recently shown to effectively describe the statical and dynamical correlation of different molecular systems. In particular, we have studied the oxygen molecule, the superoxide anion, the nitric oxide radical and anion, the hydroxyl and hydroperoxyl radicals and their corresponding anions, and the hydrotrioxyl radical. Overall, the methodology was able to correctly describe the geometrical and electronic properties of these systems, through compact but fully-optimised basis sets and with a computational cost which scales as N(3) - N(4), where N is the number of electrons. This work is therefore opening the way to the accurate study of the energetics and of the reactivity of large and complex oxygen species by first principles.
氧分子处于单线态和三线态时的电子性质，以及许多含氧化合物小分子自由基和阴离子的电子性质，在化学、生物学和大气科学的不同领域中都发挥着重要作用。然而，由于在存在一个或多个未成对电子的情况下难以正确描述静态和动态相关效应，这类物种的电子结构对从头算计算方法来说是一个挑战。只有最高水平的量子化学方法才能可靠地表征它们的分子性质，如结合能、平衡结构、分子振动、电荷分布和极化率。在这项工作中，我们使用变分蒙特卡罗（VMC）方法和晶格正则化蒙特卡罗（LRDMC）方法来研究氧气及氧活性物种的平衡几何结构和分子性质。量子蒙特卡罗方法与Jastrow反对称双电子幂（JAGP）波函数假设相结合使用，最近的研究表明该假设能有效地描述不同分子体系的静态和动态相关性。具体而言，我们研究了氧分子、超氧阴离子、一氧化氮自由基和阴离子、羟基和氢过氧自由基及其相应的阴离子，以及氢三氧自由基。总体而言，该方法能够通过紧凑但经过充分优化的基组正确描述这些体系的几何和电子性质，并且计算成本与N(3) - N(4)成比例，其中N是电子数。因此，这项工作为通过第一性原理精确研究大型复杂氧物种的能量学和反应性开辟了道路。
