Alavi Saman, Woo T K
Department of Chemistry, University of Ottawa, Ottawa, Ontario KIN 6N5, Canada.
J Chem Phys. 2007 Jan 28;126(4):044703. doi: 10.1063/1.2424936.
The stability of structure H (sH) carbon dioxide clathrate hydrates at three temperature-pressure conditions are determined by molecular dynamics simulations on a 3x3x3 sH unit cell replica. Simulations are performed at 100 K at ambient pressure, 273 K at 100 bars and also 300 K and 5.0 kbars. The small and medium cages of the sH unit cell are occupied by a single carbon dioxide guest and large cage guest occupancies of 1-5 are considered. Radial distribution functions are given for guests in the large cages and unit cell volumes and configurational energies are studied as a function of large cage CO(2) occupancy. Free energy calculations are carried out to determine the stability of clathrates for large cage occupancies at three temperature/pressure conditions stated above. At the low temperature, large cage occupancy of 5 is the most stable while at the higher temperature, the occupancy of 3 is the most favored. Calculations are also performed to show that the CO(2) sH clathrate is more stable than the methane clathrate analog. Implications on CO(2) sequestration by clathrate formation are discussed.
通过对一个3×3×3结构H（sH）二氧化碳笼形水合物晶胞复制品进行分子动力学模拟，确定了该水合物在三种温度-压力条件下的稳定性。模拟分别在常压下的100K、100巴压力下的273K以及300K和5.0千巴压力下进行。sH晶胞的小笼和中笼被单个二氧化碳客体占据，并考虑了大笼中1至5个客体占据情况。给出了大笼中客体的径向分布函数，并研究了晶胞体积和构型能量随大笼中二氧化碳占据情况的变化。进行了自由能计算，以确定在上述三种温度/压力条件下大笼不同占据情况时笼形水合物的稳定性。在低温下，大笼占据数为5时最稳定，而在较高温度下，占据数为3时最有利。计算还表明，二氧化碳sH笼形水合物比甲烷笼形水合物类似物更稳定。讨论了通过形成笼形水合物进行二氧化碳封存的意义。
