The effects of low-level PES on the overall accuracy of the final surface constructed by using hierarchical construction were investigated with the constructions of a number of global surfaces for the H3 system at UHF...The effects of low-level PES on the overall accuracy of the final surface constructed by using hierarchical construction were investigated with the constructions of a number of global surfaces for the H3 system at UHF （UMP2, DFT-B3LYP, UCCSD（T））/vtz, and UCCSD（T）/avqz levels of theory. The total reaction probabilities for the H＋H2 reaction calculated on these surfaces revealed that the accuracy of UCCSD（T）/avqz surface is very close to the well-known BKMP2 surface, while the UCCSD（T）/vtz PES has a slightly higher barrier. In contrast, the low-level theories （UHF, UMP2, DFT-B3LYP） with vtz basis set can only provide a qualitative description of this simplest reaction despite the fact that they are widely used to study reactions in complex systems. On the other hand, although these theories are not accurate on describing the reaction, they can be used to provide the low- level PESs for hierarchical construction of the UCCSD（T）/avqz PES with the number of UCCSD（T）/avqz energies substantially reduced.展开更多
The C-I bond dissociation enthalpies （BDE） of various organic iodides were calculated using high-level theoretical methods including MP2 and CCSD（T） with extrapolated basis set as well as a number of density funct...The C-I bond dissociation enthalpies （BDE） of various organic iodides were calculated using high-level theoretical methods including MP2 and CCSD（T） with extrapolated basis set as well as a number of density functional theory methods. After systematic evaluation of the theoretical results against available experimental C-I BDEs, it was found that the MPW LYPIM method gave the lowest root mean square error. We, therefore, used this method to examine the substituent effects on different categories of C（sp3）-I and C（sp2）-I bonds. Fur thermore, the remote substituent effects on the C-I BDEs of substituted iodobenzenes and substituted （iodomethyl）benzenes were also investigated at the same level. The C-I BDEs of typical heteroaromatic iodides including five-membered and six-membered heterocyclic iodides were also examined.展开更多
文摘The effects of low-level PES on the overall accuracy of the final surface constructed by using hierarchical construction were investigated with the constructions of a number of global surfaces for the H3 system at UHF （UMP2, DFT-B3LYP, UCCSD（T））/vtz, and UCCSD（T）/avqz levels of theory. The total reaction probabilities for the H＋H2 reaction calculated on these surfaces revealed that the accuracy of UCCSD（T）/avqz surface is very close to the well-known BKMP2 surface, while the UCCSD（T）/vtz PES has a slightly higher barrier. In contrast, the low-level theories （UHF, UMP2, DFT-B3LYP） with vtz basis set can only provide a qualitative description of this simplest reaction despite the fact that they are widely used to study reactions in complex systems. On the other hand, although these theories are not accurate on describing the reaction, they can be used to provide the low- level PESs for hierarchical construction of the UCCSD（T）/avqz PES with the number of UCCSD（T）/avqz energies substantially reduced.
文摘The C-I bond dissociation enthalpies （BDE） of various organic iodides were calculated using high-level theoretical methods including MP2 and CCSD（T） with extrapolated basis set as well as a number of density functional theory methods. After systematic evaluation of the theoretical results against available experimental C-I BDEs, it was found that the MPW LYPIM method gave the lowest root mean square error. We, therefore, used this method to examine the substituent effects on different categories of C（sp3）-I and C（sp2）-I bonds. Fur thermore, the remote substituent effects on the C-I BDEs of substituted iodobenzenes and substituted （iodomethyl）benzenes were also investigated at the same level. The C-I BDEs of typical heteroaromatic iodides including five-membered and six-membered heterocyclic iodides were also examined.
