We investigated the basis set convergence of high-order coupled-cluster interaction energy contributions for 21 small weakly bound complexes. By performing CCSDT(Q) calculations in at least the aug-cc-pVTZ basis set, and CCSDT calculations in at least aug-cc-pVQZ (aug-cc-pVTZ for one system), we found the convergence to be quite slow. In particular, the 6-31G*(0.25) and 6-31G**(0.25,0.15) bases...

A set of supramolecular cage-structures--spherophanes--was studied at the density functional B3LYP level. Full geometrical structure optimisations were made with 6-31G and 6-31G(d) basis sets followed by frequency calculations, and electronic energies were evaluated at B3LYP/6-31++G(d,p). Three different symmetries were considered: C1, Ci, and Oh. It was found that the bonds between the benzene...

The crystal structure of o-toluidinium chloranilate and m-toluidinium chloranilate, 2CH3C6H4NH3 · C6O4Cl22−, was determined by single crystal X-ray diffraction at room temperature. It was found that o-toluidinium chloranilate (I) is monoclinic, P21/n (#14), Z = 2, a = 5.2184(14), b = 7.825(2), c = 22.840(5) Å, and β = 92.015(19)◦ , and m-toluidinium chloranilate (II) is monoclinic, P21/c (#14),...

A method to approximate ab initio shielding constants is presented, in which the ab initio density matrix is replaced in the gauge invariant atomic orbital formalism with the density matrix resulting from an effective fragment potential calculation. The resulting first-order density matrix is then iterated to self-consistency. The method is compared with fully ab initio gauge invariant atomic o...

The structural saturation and stability, the energy gap, and the density of states of a series of small, siliconbased clusters have been studied by means of the PM3 and some ab initio ~HF/6-31G* and 6-31111G**, CIS/6-31G* and MP2/6-31G*! calculations. It is shown that in order to maintain a stable nanometric and tetrahedral silicon crystallite and remove the gap states, the saturation atom or s...

The title compound 4-(5-((4-bromobenzyl)thio)-4-phenyl-4H-1,2,4-triazol-3-yl)pyridine (C20H15BrN4S) was synthesized, and its structure was confirmed by 1H NMR, MS and elemental analyses and single-crystal X-ray structure determination. It crystallizes in the triclinic space group P-1 with a = 7.717(3), b = 9.210(3), c = 13.370(5) Å, α = 80.347(13), β = 77.471(13), γ = 89.899(16) ̋, V = 913.9(6) ...

A reação da hidroxilamina com acetato de fenila foi investigada teoricamente para se obter uma melhor compreensão do efeito alfa nas reações de nucleófilos neutros. Os cálculos foram feitos em nível B3LYP/6-311+G(2df,2p)//HF/6-31G(d) incluindo o solvente (água) em nível PCM/HF/6-31G(d). Os resultados mostram que um ataque direto da hidroxilamina leva a uma barreira de energia livre de ativação ...

Analytic gradients of dual-basis Hartree-Fock and density functional theory energies have been derived and implemented, which provide the opportunity for capturing large basis-set gradient effects at reduced cost. Suggested pairings for gradient calculations are 6-31G/6-31G**, dual[-f,-d]/cc-pVTZ, and 6-311G*/6-311 + +G(3df,3pd). Equilibrium geometries are produced within 0.0005 A of large-basi...

The stereoselectivity of reaction of methyl acrylate, methyl methacrylate and methyl transcrotonate with cyclopentadiene was studied with ab initio RHF/6-31G* and B3LYP/6-31G* levels of theory. The stereoselectivities predicted for methyl acrylate and methyl methacrylate with cyclopentadiene in the gas phase were found to be in good agreement with experimental results. The preference of endo se...

By ab initio quantum mechanical calculations on P 2 S^ its equilibrium energy, geometry and vibrational frequencies along with their PED values have been obtained. The basis sets STO-5G, 6-31G, STO-5G* and 6-31G* were employed, and force field calculations were carried out at the STO-5G and the STO-5G* levels. The calculations show that the assignment for some bands between 180 and 260 cm " 1 s...