Heit Yonaton N, Beran Gregory J O
Department of Chemistry, University of California, Riverside, California 92521, USA.
Acta Crystallogr B Struct Sci Cryst Eng Mater. 2016 Aug 1;72(Pt 4):514-29. doi: 10.1107/S2052520616005382. Epub 2016 Jul 16.
Molecular crystals expand appreciably upon heating due to both zero-point and thermal vibrational motion, yet this expansion is often neglected in molecular crystal modeling studies. Here, a quasi-harmonic approximation is coupled with fragment-based hybrid many-body interaction calculations to predict thermal expansion and finite-temperature thermochemical properties in crystalline carbon dioxide, ice Ih, acetic acid and imidazole. Fragment-based second-order Möller-Plesset perturbation theory (MP2) and coupled cluster theory with singles, doubles and perturbative triples [CCSD(T)] predict the thermal expansion and the temperature dependence of the enthalpies, entropies and Gibbs free energies of sublimation in good agreement with experiment. The errors introduced by neglecting thermal expansion in the enthalpy and entropy cancel somewhat in the Gibbs free energy. The resulting ∼ 1-2 kJ mol(-1) errors in the free energy near room temperature are comparable to or smaller than the errors expected from the electronic structure treatment, but they may be sufficiently large to affect free-energy rankings among energetically close polymorphs.
由于零点振动和热振动运动，分子晶体在加热时会显著膨胀，但这种膨胀在分子晶体建模研究中常常被忽略。在此，将准谐近似与基于片段的混合多体相互作用计算相结合，以预测结晶二氧化碳、冰Ih、乙酸和咪唑的热膨胀及有限温度下的热化学性质。基于片段的二阶Möller-Plesset微扰理论（MP2）以及含单、双激发和微扰三激发的耦合簇理论[CCSD(T)]预测的热膨胀以及升华焓、熵和吉布斯自由能的温度依赖性与实验结果吻合良好。在焓和熵中忽略热膨胀所引入的误差在吉布斯自由能中会部分抵消。在室温附近，自由能中产生的约1 - 2 kJ mol⁻¹的误差与电子结构处理预期的误差相当或更小，但它们可能大到足以影响能量相近的多晶型物之间的自由能排序。
