Water trimer cation
Water trimer cation
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水三聚体阳离子
DOI：
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
Kwang S. Kim
中科院分区：
文献类型：
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作者：
H. Lee;Kwang S. Kim
用密度泛函理论(DFT)和高能级从头算方法研究了水三聚阳离子[(H2O)3+]的结构、相互作用能、电子性质和红外光谱。比较了水三聚体阳离子的两种结构[含H3O+的线状(3Lp)结构和环状(300)结构]。对于具有单、双和微扰三重激发的耦合团簇理论的完全基组(CBS)极限[CCSD(T)]，3LP结构比3OO结构更稳定。这表明水团簇的电离产生了含氢阳离子部分(H3O+)和羟基自由基。值得注意的是，水三聚体阳离子的计算结果随计算水平的不同而变化很大。在Möler-Plesset二阶微扰理论水平上，由于低估了O…，3oo的稳定性被低估没有半键能。即使对于MP2优化几何结构上的CCSD(T)单点计算，这种稳定性也被低估了。对于3OO结构，MP2和CCSD(T)计算给出了两个O原子之间存在半键的闭环结构，而密度泛函计算由于高估了O…而给出了开环结构没有半键能。因此，为了获得可靠的水三聚体阳离子的稳定性和频率，CCSD(T)几何构型优化和频率计算是必要的。在这一点上，需要改进密度泛函以考虑适当的O…没有半键能。
By using density functional theory (DFT) and high-level ab initio theory, we have investigated the structure, interaction energy, electronic property, and IR spectra of the water trimer cation [(H2O)3+]. Two structures of the water trimer cation [the H3O+ containing linear (3Lp) structure versus the ring (3OO) structure] are compared. For the complete basis set (CBS) limit of coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)], the 3Lp structure is 11.9 kcal/mol more stable than the 3OO structure. This indicates that the ionization of water clusters produce the hydronium cation moiety (H3O+) and the hydroxyl radical. It is interesting to note that the calculation results of the water trimer cation vary seriously depending on the calculation level. At the level of Möller–Plesset second-order perturbation (MP2) theory, the stability of 3OO is underestimated due to the underestimated O…O hemibonding energy. This stability is also underestimated even for the CCSD(T) single point calculations on the MP2-optimized geometry. For the 3OO structure, the MP2 and CCSD(T) calculations give closed-ring structures with a hemi-bond between two O atoms, while the DFT calculations show open-ring structures due to the overestimated O…O hemibonding energy. Thus, in order to obtain reliable stabilities and frequencies of the water trimer cation, the CCSD(T) geometry optimizations and frequency calculations are necessary. In this regard, the DFT functionals need to be improved to take into account the proper O…O hemibonding energy.