论文标题
在冰上滑行，以寻找用于谷物的星体化学的准确且具有成本效益的计算方法：HCN异构化的令人困惑的情况
Gliding on ice in search of accurate and cost-effective computational methods for astrochemistry on grains: the puzzling case of the HCN isomerization
论文作者
论文摘要
通过植根于耦合簇ANSATZ和密度功能方法的精确复合方法（Jun-cheap）研究了氰化氢在冰粒表面上与异氰化物的异构化。在对相对较小的模型系统HCN的几何和反应能量对几何和反应能量的基准测试后，（H2O）2选择了最佳性能DFT方法。然后在QM/QM $'$方法中使用一个包含20种水分子的大集群，包括一个模仿冰冷谷物表面的现实环境。我们的结果表明，四个水分子直接参与了质子继电器机制，该机制大大降低了相对于分离的分子中发生的直接氢转移的活化能。在三层QM/QM'/mm模型的框架内，群集的大小进一步扩展到192个水分子，对统治异构化的能量屏障的影响可忽略不计。通过过渡状态理论对反应速率的计算表明，在冰的表面上，HNC与HCN的异构化即使在低温下也很容易发生，这要归功于降低的激活能量可以通过隧道有效克服。
The isomerization of hydrogen cyanide to hydrogen isocyanide on icy grain surfaces is investigated by an accurate composite method (jun-Cheap) rooted in the coupled cluster ansatz and by density functional approaches. After benchmarking density functional predictions of both geometries and reaction energies against jun-Cheap results for the relatively small model system HCN -- (H2O)2 the best performing DFT methods are selected. A large cluster containing 20 water molecules is then employed within a QM/QM$'$ approach to include a realistic environment mimicking the surface of icy grains. Our results indicate that four water molecules are directly involved in a proton relay mechanism, which strongly reduces the activation energy with respect to the direct hydrogen transfer occurring in the isolated molecule. Further extension of the size of the cluster up to 192 water molecules in the framework of a three-layer QM/QM'/MM model has a negligible effect on the energy barrier ruling the isomerization. Computation of reaction rates by transition state theory indicates that on icy surfaces the isomerization of HNC to HCN could occur quite easily even at low temperatures thanks to the reduced activation energy that can be effectively overcome by tunneling.
