After tests, the DFT PES (denoted as PESL) has the following architecture: the input adopts 3059 PIPs, the first and second hidden layers have 4 and 50 neurons. With a total of 12541 fitting parameters, the final fitting error is 0.470 kcal/mol. The scattered distribution of fitting errors for PESL is shown in Fig. , which shows that the errors are evenly distributed within the energy range from -28.8 to 120 kcal/mol. The percentages of absolute fitting errors less than 0.2, 0.4 and 0.5 kcal/mol are 50.2%, 74.8% and 81.8%, respectively. The energy distribution of the DFT data points is illustrated in Fig. , and most points fall in the energy range of 0 ~ 40 kcal/mol.