应用分子力学研究表面吸附能的可行性

Molecular mechanics(MM)study on the surface adsorption energy

为了节省计算时间和资源,研究真实体系的表面吸附问题,少数科研工作者采用分子力学研究分子的表面吸附问题。但是我们知道分子力学方法采用了“Born-Oppenheimer”近似,忽略了电子的运动,只计算与原子核位置相关的体系能量,因此不能求解与电子运动和分布相关的问题。然而表面吸附可以划分为物理吸附和化学吸附两种情况。在物理吸附过程中,分子的电子运动和分布并没有发生变化。而在化学吸附过程中,分子的电子运动和分布发生了变化。那么用分子力学来研究表面吸附中的物理吸附过程忽略化学吸附,到底会对最终的吸附分析造成多大的误差呢?用分子力学来研究表面吸附究竟是否可行呢?为了消除这些困惑,我们通过分子力学优化计算得到了TiO_2(110)表面对无机分子(H_2O,CO_2),有机小分子(CH_3OH,CHOOH,CH_2O),共轭分子(Bi-isonicotinic acid)的分子吸附能,并将这些吸附能与实验,其他量化计算(DFT,PM3)的结果进行对比。我们的数据表明,用分子力学计算得到的吸附能与实验值,量化计算值都相当接近。因此用分子力学来研究表面吸附是可行的。

In order to save the computing time and the resources, and to research real system surface adsorption question, the minority scientific research workers used the molecular mechanics to study the molecular surface adsorption question. But we knew the molecular mechanics method used the approximate of ＂Born-Oppenheimer＂, and neglected the electronic movement, only calculated the atomic nucleus position correlation system energy. Therefore it could not solve the movement and the distribution of electronic. However the surface adsorption may divide into the physisorption and the chemical adsorption. In the physisorption process, the movement and distribution of the molecular electronic has been maintained invariablely. But in the chemical adsorption process, the movement and the distribution of the molecular electronic has been changed. Then how degree the errors can be created for the final adsorption analysis when the molecular mechanics was used to study the physisorption process but do not consider the chemical adsorption？ Whether the studies of the surface adsorption with the molecular mechanics is actually feasible？ In order to eliminate these controversies, we obtained the adsorption energy of the inorganic members （ H2 O, CO2 ）, organic small members （ CH3 OH, CHOOH, CH2 O）, and conjugate member （Bi-isonicotinic acid） on the TiO2 （110） surface with the molecular mechanics optimization computation. These results were compared with the data from the experiment and the quantification computations （ DFT, PM3 ）. And the calculations coincide with DFT,PM3 and so on experiment tally well. Therefore the study of the surface adsorption with the molecular mechanics is more feasible.