Examination of DFT and TDDFT Methods II

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 113; no. 41; pp. 10873 - 10879
• Main Author: Wang, Yi-Gui
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 15.10.2009
• Subjects: A: Dynamics, Clusters, Excited States
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp9077739

We investigated the isomerization energies for C8 alkanes (n-octane and 2,2,3,3-tetra-methyl butane) and 1-X-propenes (X = CH3, F, Cl, Br) and the excited states for tropolone. The recently implemented TDDFT gradients enabled us to optimize the adiabatic excited-state structures and to obtain wave function files for excited-state electron density analyses with 25 functionals. The dispersion interactions had been found to be important for predicting the isomerization energies for n-octane and 2,2,3,3-tetra-methyl butane and for cis- and trans-1-X-propenes (X = CH3, F, Cl, Br). B3LYP failed to predict the isomerization energies for the first case but succeeded for the latter. We noticed that the integrated electron density and the merging contour values in the electron density difference plots were related to the isomerization energies; the DFT functionals (LSDA, BHandH, VSXC, and M052X) that could correctly account for the dispersion forces produced a greater electron density response for 2,2,3,3-tetramethyl butane than n-octane. Although the faster proton transfer reaction rate in the Ã1B2 excited state relative to the X̃1A1 ground state of tropolone could be reproduced only by M052X, the three newly designed functionals (BMK, CAM-B3LYP, and M052X) apparently performed better than other DFT functionals. The C−C′ bond lengths of the C s symmetry excited state were possibly underestimated by DFT methods; the underestimation of C−C′ bond lengths contributed to the high proton transfer barriers in the Ã1B2 excited state of tropolone.