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arXiv 1312.2897physics.chem-phcond-mat.mtrl-sci
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质子化水二聚体的量子Monte Carlo研究

Quantum Monte Carlo study of the protonated water dimer

Mario Dagrada, Michele Casula, Antonino M. Saitta, Sandro Sorella, Francesco Mauri

摘要:

我们报告了一个广泛的理论研究质子化水二聚体(Zundel离子)的高度相关的变分蒙特卡罗和晶格正则化蒙特卡罗方法。该系统代表了质子转移(PT)的最简单的模型和正确的描述其属性是必不可少的,以了解在更复杂的水相系统的PT机制。我们的Jastrow关联AGP波函数确保了电子关联的准确处理。利用原子杂化轨道上的原始基集收缩的优势,我们能够显着限制变分参数的数量与数值精度的系统控制,为了模拟更大的系统至关重要。我们调查的Zundel离子的能量和几何性质作为一个功能的氧-氧距离,作为反应坐标。在这两种情况下,我们的QMC结果被发现与耦合簇CCSD(T)技术,量子化学的“金标准”非常一致。对质子转移静态势垒和离解能的计算也显示出相同的一致性。与密度泛函理论(DFT)的结果在PBE近似的比较指出了电子相关的正确描述的PT在二聚体中的关键作用。我们的方法能够解决微小的能量差异(~ 0.1千卡/摩尔)和相应的结构变化,在质子转移发生;它结合了这些功能与粒子数的N^3-N^4标度(相对于其他后DFT方法有利),作为一个更大的质子化水簇的基准计算证明。这里使用的QMC方法代表了一个有前途的候选人,提供第一个高层次的从头计算描述PT在水中。

英文摘要:

We report an extensive theoretical study of the protonated water dimer (Zundel ion) by means of the highly correlated variational Monte Carlo and lattice regularized Monte Carlo approaches. This system represents the simplest model for proton transfer (PT) and a correct description of its properties is essential in order to understand the PT mechanism in more complex acqueous systems. Our Jastrow correlated AGP wave function ensures an accurate treatment of electron correlations. Exploiting the advantages of contracting the primitive basis set over atomic hybrid orbitals, we are able to limit dramatically the number of variational parameters with a systematic control on the numerical precision, crucial in order to simulate larger systems. We investigate energetics and geometrical properties of the Zundel ion as a function of the oxygen-oxygen distance, taken as reaction coordinate. In both cases, our QMC results are found in excellent agreement with coupled cluster CCSD(T) technique, the quantum chemistry "gold standard". Calculations on proton transfer static barriers and dissociation energies display the same agreement. A comparison with density functional theory (DFT) results in the PBE approximation points out the crucial role of electron correlations for a correct description of the PT in the dimer. Our method is able to resolve the tiny energy differences (~ 0.1 Kcal/mol) and the corresponding structural variations at which the proton transfer takes place; it combines these features with a N^3-N^4 scaling with number of particles (favorable with respect to other post-DFT methods), as proven by a benchmark calculation on a larger protonated water cluster. The QMC approach used here represents a promising candidate to provide the first high-level ab initio description of PT in water.

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