Calibration and comparison of the Gaussian-2, complete basis set, and density functional methods for computational thermochemistry

Petersson, G. A.; Malick, David K.; Wilson, William G.; Ochterski, Joseph W.; Montgomery, J. A.; Frisch, M. J.

doi:doi:10.1063/1.477794

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Time- and frequency-resolved coherent two-dimensional IR spectroscopy: Its complementary relationship with the coherent two-dimensional Raman scattering spectroscopy

A theoretical description of the coherent two-dimensional IR spectroscopy is presented. Two consecutive IR pulses can be used to create two consecutive vibrational coherence states. The third off-resonant optical pulse is used to probe the two-dimensional transient grating thus created and then the scattered field is measured. The corresponding nonlinear response functions are obtained in the analytic forms by assuming that the vibrational modes are weakly anharmonic Brownian oscillators. Since ...

A quantum electrodynamical treatment of second harmonic generation through phase conjugate six-wave mixing: Polarization analysis

The theory underlying a six-wave mixing experiment is developed using the methods of molecular quantum electrodynamics. This general theory allows the intensity of the second harmonic radiation generated by the six-wave process to be found for arbitrary arrangements of the generating laser beams. Several different polarization geometries are treated in detail, and comparison is made to experiments performed using near-resonant conditions. The agreement is good in all cases and allows detailed in...

We have reexamined several high-accuracy Gaussian-2, complete basis set and density functional methods for computational thermochemistry (in order of increasing speed): G2, G2(MP2), CBS-Q, G2(MP2,SVP), CBS-q, CBS-4, and B3LYP/6-311+G(3df,2p). We have employed Δ_fH2980 for the “extended G2 neutral test set” for this comparison. Several errors in previous studies have been corrected and experimental spin-orbit interactions have been included in all calculated atomic energies. The mean absolute deviations from experiment are 1.43, 1.76, 1.19, 1.64, 2.34, 2.66, and 3.43 kcal/mol, respectively. The maximum deviations from experiment are 10.6, 8.8, 8.1, 9.4, 11.4, 12.9, and 24.1 kcal/mol respectively. The species responsible for these maximum errors are in order: SiF₄, SiF₄, Cl₂C�CCl₂, F₂C�CF₂, ClF₃, ClF₃, and SiCl₄. All seven methods have relatively large errors for bonds to halogens, but these errors are sufficiently systematic to benefit from empirical corrections. After a discussion of ill conditioning in the “bond separation reaction” implementation of isodesmic reactions, we determine “isodesmic bond additivity corrections” (BACs) for several types of bonds by least-squares fits to the heats of formation for 76 organic species with up to ten carbons and a variety of heteroatoms. The mean absolute deviations are reduced from 1.49, 1.93, 1.22, 1.53, 2.28, 3.09, and 3.45 kcal/mol to 0.55, 0.57, 0.77, 0.63, 1.03, 0.98, and 1.16 kcal/mol. The maximum errors are reduced to about 3 kcal/mol for all but the DFT method (4.2 kcal/mol). The BACs are especially useful for larger molecules with many similar bonds. For example, the CBS-Q error for Cl₂C�CCl₂ is reduced from 8.1 to 3.0 kcal/mol and the CBS-4 errors for benzene and naphthalene are reduced from 10.5 and 17.5 to 2.1 and 1.6 kcal/mol, respectively. © 1998 American Institute of Physics.