The reactants, clusters, transition structures, and products for thevarious channels for the thermal decomposition of SiHkCl,, were optimized at the HF/6-31G(d) and MP2/6-31G(d,p) levels. The electron correlation contributions were calculated at the MP4/6-3 lG(d,p), MP4/6-31+G(Zdf,p), MP2/6-31 ++G(3df,3pd), and G-2 levels of theory. In the decomposition of SiH4, SiH2 + H2 is favored over SiH3 +...

A comparative study of ab initio 6-31G(*) and semiempirical modified neglect of differential overlap (MNDO) bond orders and MNDO diatomic energy contributions for the description of bond strengths in neutral and protonated glycine, diglycine, triglycine, and dialanine is presented. Good correlations were found between 6-31G(*) and MNDO bond orders and between MNDO bond orders and diatomic energ...

A conformational search of 5,12-dihydro-5,12-ethanonaphthacene-13-carbaldehyde predicted the presence of twelve conformations. The geometry of the twelve conformations established at the B3LYP/6-31G* level showed only six unique ones. Vibrational frequencies were calculated at the B3LYP/6-31G* level. The calculated vibrational frequencies enabled us to interpret the appearance of two bands corr...

This does not affect the other results presented in the paper. We are grateful to Professor Jan Jensen for bringing this issue to our attention. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers. Table 2 Comparison of AF-QM/MM and experimental chemical shifts for the H, Ca, C, and N atoms in GB3. (G.: gas phase; S.: in solution. T...

Excited-state calculations are implemented in a development version of the GPU-based TeraChem software package using the configuration interaction singles (CIS) and adiabatic linear response Tamm-Dancoff time-dependent density functional theory (TDA-TDDFT) methods. The speedup of the CIS and TDDFT methods using GPU-based electron repulsion integrals and density functional quadrature integration...

Some theoretical properties were analyzed and compared with the experimental data for Tamoxifen molecule, a drug commonly used as complementary therapy for breast cancer. The molecular structure and some chemical reactivity parameters were calculated through Density Functional Theory using different functionals, including B3LYP, PBE0, PBEPBE, TPSS, TPSSh and the M05 and M06 density functionals ...

The 1,3-dipolar cycloaddition of azomethine ylides bearing the biologically active 1,4-dihydropiridine ring to C(60) was investigated by means of quantum mechanical calculations at the semiempirical AM1 and DFT (B3LYP/6-31G) methods. The presence of two chiral centers and one chiral axis in the resulting fulleropyrrolidines leads to four possible [6,6] cycloaddition products. Formation of atrop...

In the present study, a theoretical study of 1,1-diaminohexaazidocyclotetraphophazene (DAHA) and its isomers has been performed, using quantum computational density functional theory (B3LYP and B3PW91 methods) with 6-31G* and 6-31G** basis sets implemented in Gaussian 03 program suite. Molecular structure and bonding, vibrational frequencies, Milliken population analysis, and natural bond orbit...

2-(2,4-Dimethylphenyl)-2H-benzotriazole (1) has been synthesized in a three step procedure starting from 2,4-dimethyl-N-(2-nitrophenyl)benzamide via a 5-(2,4- dimethylphenyl)-1-(2-nitrophenyl)-1H-tetrazole intermediate. Its structure and those of Tinuvin P and 2-phenyl-2H-benzotriazole (5) have been studied by multinuclear NMR (1H-, 13C- and 15N-) in solution and in the solid state. X-ray diffr...

Several modifications that have been made to the NDDO core-core interaction term and to the method of parameter optimization are described. These changes have resulted in a more complete parameter optimization, called PM6, which has, in turn, allowed 70 elements to be parameterized. The average unsigned error (AUE) between calculated and reference heats of formation for 4,492 species was 8.0 kc...