报告题目（Title）：AB INITIO MOLECULAR DYNAMICS SIMULATIONS OF SOME CHEMICALLY INTERESTING AQUEOUS SYSTEMS
报 告 人（Speaker）：Prof. Lauri Halonen (Helsinki University, Finland)
报告时间（Time）：  2019年9月23日（周一）14：00
报告地点（Place）：校本部E106
邀请人（inviter）：Prof. Malgorzata Biczysko
摘要（Abstract）：
We present the results of ab initio molecular dynamics (AIMD) simulations of the solution-air interface of aqueous lithium bromide (LiBr). We find that, in agreement with experimental data and previous simulation results with empirical polarizable force field models, Br- anions prefer to accumulate just below the first molecular water layer near the interface, while Li+ cations remain buried several molecular layers from the interface, even at very high concentration. The separation of ions has a profound effect on the average orientation of water molecules in the vicinity of the interface. We also find that the hydration number of Li+ cations in the center of the slab is about 4.7, regardless of the salt concentration. This estimate is consistent with recent experimental neutron scattering data, confirming that results from non-polarizable empirical models which consistently predict tetrahedral coordination of Li+ to 4 solvent molecules are incorrect. Consequently, disruption of the hydrogen bond network caused by Li+ may be overestimated in non-polarizable empirical models. Our results suggest that empirical models, in particular non-polarizable models, may not capture all of the properties of the solution-air interface necessary to fully understand the interfacial chemistry.

We have also performed AIMD simulations on formic acid and water molecule collisions with sulphur trioxide – water complexes. This was motivated by our interest in calculating the rate of formation of two different pre-reactive complexes for hydration of sulphur trioxide, which are known to be candidates for the main precursors for the formation of sulphuric acid in the atmosphere.b,c We are able to obtain information about dynamic and steric effects, which are omitted in customary reaction rate calculations based on geometry optimizations and transition state theory. Our calculations show that collisions enhance the reactivity of the formic acid catalysed pathway compared to the water assisted mechanism. Our results suggest that formic acid has higher impact on the formation of sulphuric acid in the atmosphere than what has been previously estimated using transition state theory.

Research  topics: Molecular  spectroscopy  including  laser  and  Fourier  transform  infrared  spectroscopy  and applications to human breath, development of new infrared laser systems, computational quantum chemistry including  density  functional  theory  of  continuous  matter  and  high-precision ab  initiocalculations  on molecules and metal clusters, atomic and molecular interactions at long distances and theoretical chemistry.