Dimethylnitramine (DMNA) is used as a model system for investigating accurate and efficient electronic structure methods for nitramines. Critical points on the potential energy surfaces of DMNA, CH3NCH3, CH3NCH2, NO2, HONO, and the transition state to HONO elimination were located through geometry optimizations using the B1LYP, B3LYP, MPW1PW91, and BH&HLYP density functional methods, in additio...

The energy at sixth-order Mnller-Plesset (MP6) perturbation theory is given and dissected into 36 sizeconsistent energy contributions resulting from single ( S ) , double ( D), triple (T ), quadruple ( Q ) , pentuple (P), and hextuple (H) excitations. It is shown that MP6 is an O ( N 9 ) method, but less costly approximations to M P ~ are possible. M P ~ is used to analyze and compare coupled c...

The insertion of SiHs into Fz has been studied with MP2, CCD, CISD and QCISD. For fluorine approaching syn to the silicon lone pair, the complex is 2.5 kcal/mol below reactants and the insertion barrier is 0.5 kcal/mol above reactants at QCISD/63 1 G*; for the anti approach, there is no barrier (only a broad plateau) and insertion proceeds with inversion at silicon. With RQCISD, both pathways g...

The a0, ax, and ac semiempirical parameters of the original Becke three-parameter method have been optimized by minimizing the difference between the density given by this method and the singles and doubles quadratic configuration interaction (QCISD) generalized density using quantum molecular similarity measures. The optimization is performed including the hybrid energy functional in a self-co...

Five multilevel model chemistries (CBS-QB3, G3B3, G3MP2B3, MCG3/3, and MC-QCISD/3) and seven hybrid density functional methods (PBE0, B1B95, B3LYP, MPW1KCIS, PBE1KCIS, and MPW1B95) have been applied to the calculation of gas-phase basicity and proton affinity values for a series of 17 molecules relevant to the study of biological phosphoryl transfer. In addition, W1 calculations were performed ...

Atomic populations and localization [lambda(A)] and delocalization [delta(A,B)] indices (LIs and DIs) are calculated for a large set of molecules at the Hartree-Fock (HF), MP2, MP4(SDQ), CISD, and QCISD levels with the 6-311++G(2d,2p) basis set. The HF method and the conventional correlation methods [MP2, MP4(SDQ), CISD, and QCISD] yield distinct sets of LIs and DIs. Yet, within the four conven...

In order to test the reliability of plane-wave and Gaussian-orbital based DFT methods for calculating reaction energies and activation barriers, detailed calculations are performed for several reactions involving gas phase silanes and a simple model of H2 desorption from the Si~100!231 surface. This study is motivated in particular by apparent discrepancies between the results of cluster-model ...

A benchmark database of forward and reverse barrier heights for 19 non-hydrogen-transfer reactions has been developed by using Weizmann 1 calculations, and 29 DFT methods and 6 ab initio wave-function theory (WFT) methods have been tested against the new database as well as against an older database for hydrogen atom transfer reactions. Among the tested hybrid DFT methods without kinetic energy...

The rearrangements for 2-phospha-4-silabicyclo[1.1.0]butane, analogous to the valence isomerization of the hydrocarbons bicyclobutane, 1,3-butadiene, and cyclobutene, were studied at the (U)QCISD(T)/6-311+G**//(U)QCISD/6-31G* level of theory. The monocyclic 1,2-dihydro-1,2-phosphasiletes are shown to be the thermodynamically preferred product, in contrast to the isomerization of the hydrocarbon...