Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061, USA.
J Phys Chem A. 2010 Sep 16;114(36):9635-43. doi: 10.1021/jp1002337.
MP2 and DFT electronic structure theories, with the functionals OPBE, OLYP, HCTH407, BhandH, and B97-1 for the latter, were used to investigate stationary point properties on the F(-) + CH(3)I → FCH(3) + I(-) potential energy surface (PES). The aug-cc-pVDZ and aug-cc-pVTZ basis sets for C, H, and F, with Wadt and Hay's 3s3p valence basis and an effective core potential (ECP) for iodine, were employed for both MP2 and DFT. Single-point CCSD(T) calculations were also performed to obtain the complete basis set (CBS) limit for the stationary point energies. The CCSD(T)/CBS reaction exothermicity is only 5.0 kJ/mol different than the experimental value. MP2 and DFT do not predict the same stationary points on the PES. MP2 predicts the C(3v) F(-)-CH(3)I and FCH(3)-I(-) ion-dipole complexes and traditional F-CH(3)-I central barrier as stationary points, as well as a C(s) hydrogen-bonded F(-)-HCH(2)I complex and a F-HCH(2)-I transition state connecting this latter complex to the F(-)-CH(3)I complex. A CCSD(T)/CBS relaxed potential energy curve, calculated for the MP2 structures, shows that going from the F(-)-CH(3)I complex to the F-CH(3)-I TS is a barrierless process, indicating these two structures are not stationary points. This is also suggested by the DFT calculations. The structures and frequencies for CH(3)I and CH(3)Cl given by MP2 and DFT are in overall good agreement with experiment. The calculations reported here indicate that the DFT/B97-1 functional gives the overall best agreement with the CCSD(T) energies, with a largest difference of only 7.5 kJ/mol for the FCH(3)-I(-) complex.
MP2 和 DFT 电子结构理论，以及用于后者的 OPBE、OLYP、HCTH407、BhandH 和 B97-1 泛函，被用于研究 F(-) + CH(3)I → FCH(3) + I(-) 势能面上的稳定点特性 (PES)。对于 C、H 和 F，使用了 aug-cc-pVDZ 和 aug-cc-pVTZ 基组，对于碘，使用了 Wadt 和 Hay 的 3s3p 价基组和有效核位势 (ECP)。MP2 和 DFT 都进行了单点 CCSD(T)计算，以获得稳定点能量的完全基组 (CBS) 极限。CCSD(T)/CBS 反应的放热仅比实验值低 5.0 kJ/mol。MP2 和 DFT 并没有在 PES 上预测到相同的稳定点。MP2 预测了 C(3v) F(-)-CH(3)I 和 FCH(3)-I(-) 离子偶极复合物以及传统的 F-CH(3)-I 中心势垒为稳定点，以及 C(s) 氢键合的 F(-)-HCH(2)I 复合物和一个 F-HCH(2)-I 过渡态，将后者复合物连接到 F(-)-CH(3)I 复合物。为 MP2 结构计算的 CCSD(T)/CBS 松弛势能曲线表明，从 F(-)-CH(3)I 复合物到 F-CH(3)-I TS 是一个无势垒过程，表明这两个结构不是稳定点。这也被 DFT 计算所证实。MP2 和 DFT 给出的 CH(3)I 和 CH(3)Cl 的结构和频率与实验总体上吻合良好。这里报道的计算表明，DFT/B97-1 泛函与 CCSD(T)能量的总体吻合度最好，对于 FCH(3)-I(-) 复合物，最大差异仅为 7.5 kJ/mol。
