| The attempt of calculating molecular enthalpies of formation theoretically has been reported for many times and the researching result is very encouraging. The calculation deviation of G2 theory is allowed within experimental deviation. It once again shows the theoretical possibility of solving practical problems. But G2 has a major shortcoming of the application which is very consuming computer machines, especially with the increasing of atomic number. Therefore, the actual application of G2 theory is impossible. In this paper, a less cost method: B3LYP was chosen to calculate enthalpies of formation of 261 molecules, and then a SVM method was using to reduce the calculated deviation.In recent years, rapid development of the Support Vector Machine (SVM) algorithm has good results in biological, chemical, drug activity and other aspects. Therefore, a combined method of B3LYP and SVM (B3LYP-SVM method) was used to calculate enthalpies of formation of 261 familiar inorganic compounds and small-to medium- sized compounds in this paper. A new lattice point search was used instead of the LOO cross-validation which was used popularly before when choosing the three parameters which control the performance of SVM for regression. When calculating, the data was randomly separated into two parts: 195 for training set and 66 for test set. The resulting mean absolute deviation (MAD) and maximum deviation (MD) for training set were 1.51 kcal/mol and 9.23 kcal/mol (correlation coefficient R=0.9995), and for test set they became to 1.78 kcal/mol and 7.31 kcal/mol (R=0.9990). And for the all 261 molecules, MAD and MD were 1.58 kcal/mol and 9.23 kcal/mol. The MAD of 177 organic compounds was reduced to 1.47kcal/mol. The result of B3LYP-SVM method is achieved G2 theory, and also allowed within the experimental deviation levels. But greatly reduce the computation time. It shows that the B3LYP-SVM method could be used as a tool for the enthalpies of formation of small- to medium- sized molecules.
|
PDF Full Text Request