Department of Chemistry, IFM, Linköping University, SE-58183 Linköping, Sweden.
J Phys Chem A. 2011 Jun 16;115(23):6169-76. doi: 10.1021/jp111328v. Epub 2011 Feb 22.
Methane hydrates with the three clathrate structures I, II, and H are studied by quantum-chemical methods. Hybrid density-functional theory B3LYP computations using periodic boundary conditions are combined with force-field methods for the thermal energy effects to calculate energetic, thermodynamic, and structural properties. The pressure dependencies for the crystal structures, lattice energies, and guest molecule interactions are derived. The quantum-chemical geometry optimizations predict too small cell volumes as compared to experimental data, but by including zero-point energy and thermal energy effects, we find the cell volumes increase and the correct densities are obtained. The phase transition from MH-I to ice Ih and methane was computed and found to occur at about 9.7 MPa.
本文采用量子化学方法研究了具有 I、II 和 H 三种笼型结构的甲烷水合物。通过使用周期性边界条件的杂化密度泛函理论 B3LYP 计算，结合力场方法研究了热能效应，以计算能量、热力学和结构性质。本文推导了晶体结构、晶格能和客体分子相互作用的压力依赖性。量子化学几何优化预测的细胞体积与实验数据相比太小，但通过包含零点能和热能效应，我们发现细胞体积增加，并得到了正确的密度。计算了从 MH-I 到冰 Ih 和甲烷的相转变，发现其发生在约 9.7 MPa。
