Doughan D I, Raff L M, Rockley M G, Hagan M, Agrawal Paras M, Komanduri R
Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078, USA.
J Chem Phys. 2006 Feb 7;124(5):054321. doi: 10.1063/1.2162170.
The reaction dynamics of vibrationally excited vinyl bromide have been investigated using classical trajectory methods on a neural network potential surface that is fitted to an ab initio database of 12 122 configuration energies obtained from electronic structure calculations conducted at the MP4(SDQ) level of theory using a 6-31G(d,p) basis set for the carbon and hydrogen atoms and Huzinaga's (43334334) basis set augmented with split outer s and p orbitals (4332143214) and a polarization f orbital with an exponent of 0.5 for the bromine atom. The sampling of the 12-dimensional configuration hyperspace of vinyl bromide prior to execution of the electronic structure calculations is accomplished by combining novelty-sampling methods, chemical intuition, and trajectory sampling on empirical and neural network surfaces. The final potential is obtained using a two-layer feed-forward neural network comprising 38 and 1 neurons, respectively, with hyperbolic tangent sigmoid and linear transfer functions in the hidden and output layers, respectively. The fitting is accomplished using the Levenberg-Marquardt algorithm with early stopping and Bayesian regularization methods to avoid overfitting. The interpolated potentials have a standard deviation from the ab initio results of 0.0578 eV, which is within the range generally regarded as "chemical accuracy" for the purposes of electronic structure calculations. It is shown that the potential surface may be easily and conveniently transferred from one research group to another. The files required for transfer of the vinyl bromide surface can be obtained from the Electronic Physics Auxiliary Publication Service. Total dissociation rate coefficients for vinyl bromide are obtained at five different excitation energies between 4.50 and 6.44 eV. Branching ratios into each of the six open reaction channels are computed at 24 vibrational energies in the range between 4.00 and 6.44 eV. The distribution of vibrational energies in HBr formed via three-center dissociation from vinyl bromide is determined and compared with previous theoretical and experimental results. It is concluded that the combination of ab initio electronic structure calculations, novelty sampling with chemical intuition and trajectories on empirical analytic surfaces, and feed-forward neural networks provides a viable framework in which to execute purely ab initio molecular-dynamics studies on complex systems with multiple open reaction channels.
利用经典轨迹方法，在神经网络势能面上研究了振动激发的溴乙烯的反应动力学。该神经网络势能面拟合了一个从头算数据库，该数据库包含12122个构型能量，这些能量是通过在理论的MP4(SDQ)水平上进行电子结构计算得到的，计算中碳原子和氢原子使用6-31G(d,p)基组，溴原子使用Huzinaga基组(43334334)并增加了分裂外层s和p轨道(4332143214)以及一个指数为0.5的极化f轨道。在进行电子结构计算之前，通过结合新颖性采样方法、化学直觉以及在经验和神经网络表面上的轨迹采样，对溴乙烯的12维构型超空间进行采样。最终的势能是使用一个两层前馈神经网络获得的，该网络分别包含38个和1个神经元，隐藏层和输出层分别使用双曲正切Sigmoid函数和线性传递函数。使用Levenberg-Marquardt算法并结合早期停止和贝叶斯正则化方法进行拟合，以避免过拟合。插值势能与从头算结果的标准偏差为0.0578 eV，就电子结构计算而言，该偏差在通常被视为“化学精度”的范围内。结果表明，该势能面可以轻松方便地从一个研究小组转移到另一个研究小组。转移溴乙烯表面所需的文件可从电子物理辅助出版服务处获得。在4.50至6.44 eV的五个不同激发能量下获得了溴乙烯的总解离速率系数。在4.00至6.44 eV范围内的24个振动能量下计算了进入六个开放反应通道中每个通道的分支比。确定了通过溴乙烯的三中心解离形成的HBr中振动能量的分布，并与先前的理论和实验结果进行了比较。得出的结论是，从头算电子结构计算、结合化学直觉的新颖性采样以及在经验解析表面上的轨迹采样和前馈神经网络的结合，为对具有多个开放反应通道的复杂系统进行纯从头算分子动力学研究提供了一个可行的框架。
