【摘要】 采用H artree-Fork,4种DFT(BLYP,B3LYP,M PW 1PW 91,SVWN 5)和M P2方法研究了甲烷水合物结构-I的氢键和范德华能.甲烷分子取HF/6-31G(d,p)优化构型,水分子选用ST 2模型.水分子间的氢键能Ehb(l)和甲烷-水分子间的范德华能EvdW(l)作为正十二面体边长l的函数,用HF/6-31G(d,p)和4种DFT方法做计算,保持水分子和甲烷分子的构型不变,在几个关键点上选用M P2方法做了计算.计算中选用6-31G(d,p)基组,分别用完全平衡校正和不完全校正法进行校正,这两种方法给出了基组重叠误差(BSSE)的上限和下限.DFT/B3LYP方法计算的氧-氧距离RO-O=0.280 nm和碳-氧距离RC-O=0.392 nm最接近于实验值0.282 nm和0.395 nm.所有计算方法(HF,DFT,M P2)都表明,甲烷水合物结构-I是一个由超强氢键(30~36 kJ/m o l)组成的稳定结构,其氢键能远大于水分子二聚体和冰I4晶格中的氢键能((-22.6±2.9)kJ/m o l和(-21.7±0.5)kJ/m o l).这些数据为气体水合物的Lennand-Jones和K ihara势能函数提供了基本参数,可用于气体水合物的分子动力学模拟.更多还原

【Abstract】 Hartree-Fock,DFT（BLYP,B3LYP,MPW1PW91,and SVWN5） and MP2 methods are used to study the intermolecular potential functions for the unit cell of methane hydrate structure-I.The unit cell is treated as a regular dodecahedron including 20 water molecules and a methane molecule in the center.The geometry of methane is optimized by ab initio HF/6-31G（d,p） and the water molecules take the geometry of an ST2 model.The water-water hydrogen bond potential E_hb（l） and water-methane van der Waals potential E_vdW（l） as functions of the side length l are calculated,keeping the molecular geometries of water and methane fixed.Then MP2 calculations are performed at several key points.In all calculations we use the 6-31G（d,p） basis set. Basis set superposition error（BSSE） is corrected and the upper and lower limits of BSSE are determined for the water-water hydrogen bond energy.The oxygenoxygen distance R_O-O=0.280 nm,and the carbon-oxygen distance R_C-O=0.392 nm obtained by BSSE-corrected B3LYP are closer to the experimental values 0.282 nm and 0.395 nm,comparing with other methods.The results indicate that the water-water pair hydrogen bond energy（30³6 kJ/mol） in gas hydrate structure-I is stronger than the hydrogen bond energy（-22.6±2.9） kJ/mol in the water dimer（H₂O）₂ and（21.7±（0.5）） kJ/mol in hexagonal ice,and the dodecahedron cell is a stable unit.These molecular interaction potentials provide a solid basis for the derivation of parameters in the Lennard-Jones 6-12 and Kihara potentials,which are useful in molecular dynamics simulations of gas hydrates.更多还原