RESUMO
The corrected Hohenberg-Kohn-Sham and corrected Harris total energy functionals recently proposed [B. Zhou and Y. A. Wang, J. Chem. Phys. 128, 084101 (2008)] have been generalized to the Hartree-Fock method. We have tested the functionals on a few molecular systems and found them to be very useful in accelerating the convergence of the total energy during a self-consistent field process.
RESUMO
Pyridinethiones are important ligand precursors of coordination complexes of therapeutic value. In aqueous solution, pyridinethiones can dimerize and tautomerize to the corresponding thiols. However, the tautomerism of pyridinethiones, which can impact on therapeutic performance, is yet not fully understood. To resolve this important issue, we have carried out ab initio and DFT calculations to compute the geometries, energies, dipole moments, and NMR, IR, and UV-vis spectroscopic properties of all possible tautomers of pyridinethiones and compared our theoretical results with the existing experimental data. We found that the thione form of the tautomer is dominant for monomers of the pyridinethiones studied here. This work can serve as a reference for exploring other similar organosulfur compounds.
RESUMO
The geometries, chemical shifts, aromaticity, and reactivity of finite-length open-ended armchair single-walled carbon nanotubes (SWCNTs) have been studied within density functional theory. The widely used model of capping hydrogen atoms at the open ends of a SWCNT changes the chemical activity of the SWCNT and destabilizes the frontier molecular orbitals. The edge pi-orbital of the open ends enhances both pi- and sigma-aromaticity of the first belt of hexagons of carbon atoms at the open ends. The effect of the open ends on the structure and chemical reactivity of the SWCNT reaches only the first several layers of the hexagons of carbon atoms. Additions of carbene and dichlorocarbene to the nanotube reveal that the open ends have higher reactivities than the inner regions.