水分子团簇与水合胞嘧啶分子的量化计算

The quantum chemistry calculations about water clusters and hydrated cytosine

根据量子化学理论,采用HF和密度泛函理论B3LYP方法,分别在6-31G(d)及6-31G(d,p)基组水平上研究了水分子团簇(H2O)n(n=1～6)及水合胞嘧啶分子Cytosine-(H2O)n(n=1～3)的基态结构及红外光谱。计算结果表明,采用相同的方法时,用6-31G(d,p)基组得到的水分子团簇基态结构相对稳定。采用相同6-31G(d)基组水平时,B3LYP/6-31G(d)方法优化的水分子团簇的基态结构要比HF/6-31G(d)得到的稳定。对结合能的计算表明,随着水分子数目的增加,水分子团簇和不同尺度的水合胞嘧啶分子的结合能都逐渐增大,结构也越来越稳定。红外光谱的计算表明,水分子团簇红外光谱最强吸收峰对应的振动模式一般是由水分子与水分子之间相互摆动形成或者某个水分子中H原子与相邻水分子中的O原子的伸缩振动形成。胞嘧啶及水合胞嘧啶分子红外光谱最强吸收峰对应的频率值随水分子数目的增加逐渐降低,水分子与胞嘧啶分子之间的氢键作用及水分子自身的摆动对振动模式的强度有一定影响。

The ground state structures and infrared spectrum of water clusters and hydrated cytosine are studied by Hartree-Fock and density functional theory on the levels of 6 -31G （d） and 6 -31 G （d, p）. It is found that ap- plying the same method, the ground state structures of water clusters obtained by 6 - 31G （ d, p） base set are more stable. Applying the same 6 -31G （d） base set, B3LYP gives the more stable structure of the water clusters. The calculations of the binding energies indicate that the binding energies of water clusters and hydrated cytosine in- crease when the number of water molecule increases. The calculated infrared spectrum shows that for water clus- ters, the strongest absorption peak corresponding to the mutual swing among water molecules and the stretch oscilla- tion between the Oxygen atom belonging to one water molecule and the Hydrogen atom in the neighboring one. Fur- thermore,it is shown that the frequencies corresponding to the strongest absorption peaks of cytosine and hydrated cytosine decrease when the number of the water molecule increases and the hydrogen bonds between the water mole- cule and cytosine and the swing belongs to the water molecule really effects on the vibration intensities.