Quantum Chemical Calculation of the Monoaminocarbonic Acids

For the first time quantum chemical MNDO method has been used for the calculation of a classical row of monoaminocarbonic acids of glycines, α-alanines, β-alanines, valines, isoleucines, norvalines and γ–aminobutyric acids, leucines and phenylalanines. The optimized geometrical and electronic structure of these compounds has been received.

On the Structure of Lead(II) Complexes in Aqueous Solutions. III. Hexanuclear Clusters

Optimum geometries based on experimental structures and corresponding electronic structures of [Pb6(μ3-OH)8]4+ and [Pb6O(μ3-OH)6]4+ clusters as well as of their hydrated [Pb6(μ3-OH)8(H2O)6]4+ and [Pb6O(μ3-OH)6(H2O)6]4+ analogues are investigated using the semiempirical MNDO method of quantum chemistry. Direct Pb-Pb and O-O bonds are vanishing in the systems under study. Small differences in interatomic Pb-Pb and Pb-O distances between these clusters indicate that they cannot be distinguished by recent experimental techniques in solution. Both the mentioned structures are stable and might coexist in solution.

On the Reliability of the Structures of Lead(II) Hydroxo Complexes Obtained by MNDO Method

Optimum geometry of tetrahedro-Pb4[(μ3-OH)4]4+ cluster obtained by the semiempirical MNDO method corresponds to Td symmetry. The calculated Pb-Pb (3.70 · 10-10 m) and Pb-O (2.33 · 10-10 m) distances are in reasonable agreement with experimental X-ray data. Additional H2O inclusion makes the agreement worse.

The Chemisorption of C on Al(111)

The chemisorption of C atoms on Al(111) was studied by means of the semiempirical MNDO method. The incorporation of the C adatom into the clusters was considered and the most favorable chemisorption site was evaluated. The hcp in-surface site was identified as the most stable adsorption site, in agreement with recent scanning tunneling microscopy (STM) experiments. This fact allowed us to use the MNDO method to evaluate the interaction energy of two chemisorbed C atoms in order to understand the observed formation of an ordered carbon underlayer. The low mobility of single isolated C adatoms revealed in STM experiments is also discussed.