Structures, energetics, vibrational spectra of NH4+ (H2O)(n=4,6) clusters: Ab initio calculations and first principles molecular dynamics simulations.
Structures, energetics, vibrational spectra of NH4+ (H2O)(n=4,6) clusters: Ab initio calculations and first principles molecular dynamics simulations.
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DOI：
10.1063/1.2943671
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发表时间：
2008-06
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影响因子：
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通讯作者：
S. Karthikeyan;Jitender Singh;Mina Park;Rajesh Kumar;Kwang Soo Kim
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文献类型：
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作者：
S. Karthikeyan;Jitender Singh;Mina Park;Rajesh Kumar;Kwang Soo Kim
利用密度泛函理论、Moller-Plesset二阶微扰理论和单、双、三摄动耦合簇理论研究了nh4 (+)(H(2)O)（n=4,6）的重要结构异构体[CCSD(T)]。为了识别NH(4) (+)(H(2)O)（n=4,6）的低能结构，需要对CCSD(T)结合能和自由能的完全基集极限进行零点能量（ZPE）修正，否则最可能的结构可能会被分配错误的结构。对于NH(4) (+)(H(2)O)(6)，笼型结构在ZPE校正前比先前报道的开放式结构更稳定，但在ZPE校正后稳定性下降。在Car-Parrinello分子动力学模拟的第一性原理中，在100 K左右，NH(4) (+)(H(2)O)(4)的三个最低能异构体和NH(4) (+)(H(2)O)(6)的两个最低能异构体的组合功率谱解释了每个实验红外光谱。
Important structural isomers of NH(4) (+)(H(2)O)(n=4,6) have been studied by using density functional theory, Moller-Plesset second order perturbation theory, and coupled-cluster theory with single, double, and perturbative triple excitations [CCSD(T)]. The zero-point energy (ZPE) correction to the complete basis set limit of the CCSD(T) binding energies and free energies is necessary to identify the low energy structures for NH(4) (+)(H(2)O)(n=4,6) because otherwise wrong structures could be assigned for the most probable structures. For NH(4) (+)(H(2)O)(6), the cage-type structure, which is more stable than the previously reported open structure before the ZPE correction, turns out to be less stable after the ZPE correction. In first principles Car-Parrinello molecular dynamics simulations around 100 K, the combined power spectrum of three lowest energy isomers of NH(4) (+)(H(2)O)(4) and two lowest energy isomers of NH(4) (+)(H(2)O)(6) explains each experimental IR spectrum.