Transferability of pairwise atom potential parameters: a test on the structural calculation of the glyoxal-Ar complex isomers

摘要

The pairwise atom potential approach for calculating intermolecular potential energy surfaces is tested on the glyoxal-Ar complex with three isomeric structures. Potential parameters of the Ar-H, Ar-C and Ar-O pairs were extracted from fittings to the experimentally determined H_2-Ar and CO_2-Ar potential surfaces. It is found that when an anisotropic term reflecting the π electron distribution in the CO chromophore is added, the pair-potential calculation can generate three potential minima with reasonable energies and van der Waals stretching frequencies mimicking the three experimentally observed structures. The electronically excited complex parameters extracted from an ab initio calculation done for H_2CO(A)-Ar can predict the shift of the Ar position upon electronic excitation of glyoxal. These observations indicate the transferability of properly determined pair potential parameters from one molecular system to another and the importance of anisotropy which reflects the electron density spatial distribution. The effectiveness of the pairwise atom approach for performing expedient, approximate intermolecular potential calculations is also evident, although its usefulness for generating accurate potential surfaces has yet to be tested.