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Applied Physics
Vol. 10  No. 05 ( 2020 ), Article ID: 35659 , 5 pages
10.12677/APP.2020.105036

The Stabilities of Stacked Cyclic Pentamers of (H2O)10 Cluster

Huihui Yang*, Yuxin Chen

School of Science, Xi’an Aeronautical University, Xi’an Shaanxi

Received: Apr. 30th, 2020; accepted: May 13th, 2020; published: May 20th, 2020

ABSTRACT

In this paper, the structures of stacked cyclic pentamers of (H2O)10 clusters are optimized, and the stabilities are compared, and the vibrational frequencies are calculated. The calculations show that the structure of five stacked cyclic pentamers of (H2O)10 is almost degenerate. In the lowest energy structure, the hydrogen bonding direction in two cyclic pentamers is opposite. The calculation and analysis of the vibrational frequencies show that the bending vibrations of H-O-H and the stretching vibration of O-H which involved in the formation of hydrogen bond are different.

Keywords:(H2O)10, Ab Initio Calculation, Stabilities, Vibration Spectrum

(H2O)10团簇双层五元环结构稳定性的研究

杨慧慧*，陈雨欣

西安航空学院，理学院，陕西 西安

收稿日期：2020年4月30日；录用日期：2020年5月13日；发布日期：2020年5月20日

摘 要

本文优化了(H2O)10团簇的五个双层五元环结构，比较了其稳定性，并计算了其振动频率。计算表明五个双层五元环结构几乎是简并的，当其中一层五元环中OH…O是逆时针连接，另一层是顺时针，两层五元环中氢键连接方向相反时，团簇结构能量较低。对频率计算分析表明氢键的连接方式不同，使H2O中H-O-H的弯曲振动和参与形成氢键的O-H伸缩振动不同。

关键词 :(H2O)10团簇，从头计算，稳定性，振动光谱

Copyright © 2020 by author(s) and Hans Publishers Inc.

This work is licensed under the Creative Commons Attribution International License (CC BY 4.0).

http://creativecommons.org/licenses/by/4.0/

1. 引言

水分子是最简单的分子之一，同时也是我们最熟悉又陌生的分子。由于水分子独特的电子结构，它不仅具有大的偶极距(1.83 D)，还能同时参与形成四个氢键，这使得这一特别稳定的分子同时也非常活泼。水分子的这一特性不仅使凝聚相的水具有奇特而丰富的性质，也决定了水溶液的性质以及它在生命现象中的特殊作用。氢键的强度(0.1~0.7 eV)介于弱的范德华作用和强的化学键之间，对于它的理解既需要在分子轨道水平来认识，同时理论处理又要求有很高的精度，这使得我们对水这一简单又复杂的小分子仍缺乏很好的认识。

过去三十年人们对水分子团簇从实验和理论方面进行了大量研究，这不仅是水团簇本身具有很多重要性质，更主要的是它为高精度的从头计算提供了重要的研究对象，而这种研究对于人们认识水分子之间的相互作用和凝聚相性质、溶液化学以及许多生物过程具有重要价值 [1] [2] [3]。从实验研究讲，红外和远红外振转隧穿光谱确切地表明3~5个水分子形成环状结构并观测到六聚水的多个异构体 [4] [5] [6]，对包含7~10个水分子的纯水团簇和水合物也有相关实验研究 [7] [8] [9] [10]。理论研究方面，利用无偏全局能量最小搜索方法(Basin Hopping, Monte Carlo, Genetic Algorithm)结合各种经验势函数对水分子的最稳定结构进行了大量研究 [11] [12] [13] [14] [15]，同时利用不同从头计算方法对最稳定结构进行确认并研究其中的氢键性质 [16] [17] [18] [19] [20]。有关水分子团簇的结构，Xantheas等人最近进行了综述 [21] [22]。大部分经验势确定(H2O)10的最稳定结构是双层五元环，经验势TIP3P给出的是一个蝴蝶型结构；不同精度的从头计算表明双层五元环的能量更低。Buck [9] 认为(H2O)10的红外光谱支持蝴蝶结构，但是实验光谱与理论计算的光谱比对发现实验光谱与蝴蝶结构的光谱也有很大差别。本文利用不同精度的从头计算方法计算了五个(H2O)10团簇的双层五元环结构，比较了其稳定性。

2. 计算方法

初始结构来自相关文献及Wales等人提供的数据库 [16] [23]。为了能对氢键给出比较可靠的描述，要求计算方法能较好的处理电子相关。之前的研究表明，B3LYP/6-31G(d,p)给出的结合能远大于其它方法给出的结果，且优化得到的结构也较其它方法确定的结构有较大畸变。和组态相互作用及耦合簇方法相比，多体微扰方法的计算量较小，且对水分子团簇的计算能给出可靠的结果。由于氢键键长较大(OH…O约1.8 Å，O…O距离约2.8 Å)，在水团簇的计算中基函数的选取必须要包括极化函数。我们在计算中采用二级微扰理论MP2 [24]，基组选取加入极化函数的双ζ6-311G(d,p)和aug-cc-pVDZ。计算采用的是Gaussian09程序。

3. 结果讨论

图1给出了五个(H2O)10团簇的双层五元环结构，分别用W10-1、W10-2、W10-3、W10-4和W10-5表示。结构W10-1和W10-2中层与层之间的氢键连接方式完全一致，而上层五元环中的氢键连接方式不同，W10-1上层氢键OH…O是逆时针连接，下层顺时针，两层五元环中氢键连接方向相反，W10-2中上下两层五元环中氢键连接方向相同，都是顺时针，W10-1的能量更低。结构W10-3、W10-4和W10-5中层与层之间的氢键连接方式及五元环中的氢键连接方式都各不相同。

Figure 1. The different isomers of (H2O)10 cluster

图1. (H2O)10团簇不同的双层五元环结构

采用MP2方法，两个不同的基组6-311G(d,p)和aug-cc-pVDZ计算的(H2O)10团簇的双层五元环结构的能量在表1中给出。两种基组计算的不同异构体的稳定性顺序非常一致，从表1可看出，W10-1和W10-2能量非常一致，几乎是简并的，W10-3、W10-4和W10-5的能量一致，比W10-1和W10-2略高，五个异构体的能量都非常接近。两种不同基组计算的稳定性完全一致。由于五个异构体的能量差异非常小，为了更直观的呈现不同异构体的差异，分析能量存在微小差异的原因，我们还计算了不同结构的振动光谱，其结果在图2中给出，图中红色方框标记了振动光谱不同的部分。振动不同的部分频率较低的振动对应是H2O中H-O-H的弯曲振动，频率较高的是五元环中参与形成氢键的O-H的伸缩振动。由于不同异构体中氢键的连接方式不同导致稳定性不同，同时也使H2O中H-O-H的弯曲振动和参与形成氢键的O-H伸缩振动不同，但不影响未参与形成氢键的O-H伸缩振动。

Table 1. The energies of (H2O)10 clusters calculated using MP2 with 6-311G(d,p) and aug-cc-pVDZ

表1. MP2方法不同基组计算的(H2O)10团簇的能量

Figure 2. The IR spectrum of (H2O)10 clusters

图2. (H2O)10团簇的双层五元环结构的振动光谱

4. 小结

本文采用MP2方法两种不同的基组6-311G(d,p)和aug-cc-pVDZ优化了五个(H2O)10团簇的双层五元环结构，并计算了其振动频率。结果表明五个五元环结构的能量非常一致，当上下两层五元环中氢键连接方向相反时，结构最稳定，频率计算分析表明，由于五元环和层层之间的氢键连接方式不同，水分子中O-H-O的弯曲振动和参与形成氢键的O-H伸缩振动频率明显不同，但五个五元环中未参与形成氢键的O-H伸缩振动的频率一致。

基金项目

大学生创新创业训练项目(S201911736023，DCX2019043)，西安航空学院校级科研项目(2018KY0207)。

文章引用

杨慧慧,陈雨欣. (H2O)10团簇双层五元环结构稳定性的研究
The Stabilities of Stacked Cyclic Pentamers of (H2O)10 Cluster[J]. 应用物理, 2020, 10(05): 281-285. https://doi.org/10.12677/APP.2020.105036

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    25. NOTES

    *通讯作者。

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