| Summary: | 博士 === 國立中正大學 === 化學所 === 98 === This Ph. D. thesis consists of five chapters. In chapter 1, we improved the accuracy of density functional methods by combining energies calculated using more than one basis sets and this was called the multi-coefficient density functional theory or MC?DFT. We tested the performance on updated training sets of 109 atomization energies, 38 hydrogen-transfer barrier heights, 38 non-hydrogen-transfer barrier heights, 13 ionization potentials, and 13 electron affinities. The results indicated that in most cases the accuracy can be significantly improved using more than one basis sets in the DFT calculation . In addition, the same level of accuracy can be reached using less expensive basis set combinations. The best method , the M06-2X functional using the cc-pVDZ/cc-pVTZ/aug-cc-pVDZ basis set combination, we achieved an average accuracy of 1.46 kcal/mol on training sets. For the B2K-PLYP, B2T-PLYP using the pc1/pc2/ aug-pc1 basis set combination, achieved an average accuracy of 1.50 , 1.47 kcal/mol on the same set. We expected that the MC?DFT methods can easily be applied to many types of interesting chemical systems with 10?30 heavy atoms.
In chapter 2, we have developed a new method called multicoefficient doubly-hybrid DFT (MC?DHDFT). We tested the performance on updated training sets of 109 atomization energies, 38 hydrogen-transfer barrier heights, 38 non-hydrogen-transfer barrier heights, 13 ionization potentials, and 13 electron affinities. The best method was found to be MC-DHBB95 which used the cc-pVDZ /cc-pVTZ/aug-cc-pVDZ basis set combination. The mean unsigned error was 1.51 kcal/mol on training sets and 0.69 kcal/mol on thermochemical kinetics. By using Pople type basis set the best method was MC-DHBB95 using the 6-31G(d)/MG3S basis set combination. The mean unsigned errors was 1.85 kcal/mol on training sets
In chapter 3, we presented a theoretical study on the double proton transfer dynamics of the 11-propyl-6H-indolo- [2,3-b] quinoline(6HIQ) /7-azaindole (7AI) hydrogen-bonded hetero-dimer in both the ground and electronically lowest lying excited state. The double proton transfer was concluded to undergo a concerted-asynchronous pathway. In the first electronically excited state, both CIS and TD-M06-2X theory predicted the pyrrolyl proton of 7-AI moved to the pyridinyl site of the 6HIQ, then the pyrrolyl proton of 6-HIQ moved to the pyridinyl site of the 7-AI. But these lower-level methods were unable to obtain very accurate relative energies in the proton-transfer region on first excited state. Higher-level theory (EOM?CCSD) suggested the pyrrolyl proton of 6-HIQ moved to the pyridinyl site of the 7-AI first, then the pyrrolyl proton of 7-AI moved to the pyridinyl site of the 6HIQ. The EOM?CCSD theory did not predict the intermediates on the pathway. The barrier calculated by EOM?CCSD theory was 6.1 kcal/mol which after zero-point correlation (3.3 kcal/mol), was consistent with the experimentally derived value (2.9 kcal/mol).
In chapter 4, we used the dual-level variational transition state theory with multidimensional tunneling to calculate the rate constants of the reaction for cyclic ozone ? bent-ozone. The calculated temperature range was from 25 K to 500 K. The high-level potential energy surface data were obtained from the calculation using the MRCISD+Q theory with the aug-cc-pVQZ basis set, while the low-level reaction path information was obtained using the hybrid density functional theory B3LYP with the aug-cc-pVTZ basis set. The calculated results showed very significant tunneling effects below 300 K. The half-life of the cyclic ozone was estimated 4670 seconds at 250 K and 106 seconds at 300 K. The kinetic isotope effects (kO16/k O18) were also calculated as a function of temperature, and were as high as 11 at low temperature. The calculated results suggested that cyclic-ozone may be detectable below 250 K.
In chapter 5 we used the dual-level variational transition state theory with multidimensional tunneling to calculate the rate constants of various alkyl iodides with cyanide ion. The calculated temperature range was from 100 K to 500 K. The results showed that variational effects and tunneling effects are not significant for the SN2 channel. However, the tunneling effects were important on the E2 channel. The reactions of CH3I + CN?, C2H5I + CN?, and C3H7I + CN??were found to proceed by SN2 channel. The kinetic isotope effects (KIEs) of CH3I + CN?, C2H5I + CN?, and C3H7I + CN??were calculated to be 0.88, 0.94, and 0.94, respectively. The reaction of C4H9I + CN? was predicted to proceed by the E2 channel. The KIEs was predicted to be 7.44, which is in good agreement with the experimental data.
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