Here, we analyze the possibility of predicting local and global current densities in a series of bicyclic hydrocarbons with 4n and 4n+2 -electrons from the nucleus-independent chemical shifts (NICS) computations....

Recently, we reported a series of global minima whose structures consist of carbon rings decorated with heavier group 14 elements. Interestingly, these structures feature planar tetracoordinate carbons (ptCs) and result from the replacement of five or six protons (H+) from the cyclopentadienyl anion (C5H5−) or the pentalene dianion (C8H62−) by three or four E2+ dications (E = Si–Pb), respectively. The silicon derivatives of these series are the Si3C5 and Si4C8 clusters. Here we show that ptC persists in some clusters with an equivalent number of C and Si atoms, i.e., Si5C5, Si8C8, and Si9C9. In all these species, the ptC is embedded in a pentagonal C5 ring and participates in a three-center, two-electron (3c-2e) Si-ptC-Si σ-bond. Furthermore, these clusters are π-aromatic species according to chemical bonding analysis and magnetic criteria.

Jes us S anchez-M arquez, and Manuel Fern andez-N uñez Simplified Box Orbitals (SBO) are a kind of spatially restricted basis functions. SBOs have a similar use and value to Slater functions but, because they fulfill a version of the zerodifferential overlap approximation, they allow for a drastic reduction in the number of two-electron integrals to be calculated when dealing with huge systems, and they seem to be specially adapted to study confined systems such as molecules in solution. In a previous study, the mathematical shape of SBOs was discussed and the necessary parameters were obtained by means of the variational method. In the present study, the parameters of each SBO were obtained by applying the condition that it is as similar as possible to the STO that would be used in a basis set without spatial restrictions. We have developed a method to achieve this likeness and deduced simple formulas to describe all the SBOs of any atom. We also present the SBO-3G expansions of the SBOs obtained, making it possible to use these SBOs with standard quantum chemistry calculation software. Simple formulas were also deduced to directly write the SBOs and SBO-3G corresponding to the atoms with a Z value of between 1 and 18. Finally, as a first example of the usefulness of this kind of functions, an optimized SBO-3G basis set is proposed for atoms from H to Cl in molecules.

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We analyze some procedures to introduce the effect of confining the electrons of the hydrogen atoms in cavitation spheres like those used in the self-consistent reaction field models for studying the solvent influence on molecular properties [as polarizable continuum model (PCM), or conductor screening model (COSMO)]. We have found that the boundary conditions to be applied have an important effect on the system energy that by no means should be neglected in this type of calculations. We have found as well that "-nG" expansion technique could be applicable in this kind of calculations (even at the very simple "-3G" level) and lead us to a relatively simple form of applying the theory. Moreover, we have found a way to define the cavitation radius of PCM calculations, by minimizing the system energy with respect to this parameter, which could be a more satisfactory procedure-at least from a theoretical point of view-than the use of empirical values characteristic of most of the PCM or COSMO standard calculations.