RESUMO
In this work we define a shape entropy by calculating the Shannon's entropy of the shape function. This shape entropy and its linear response to the change in the total number of electrons of the molecule are explored as descriptors of bonding properties. Calculations on selected molecular systems were performed. According to these, shape entropy properly describes electron delocalization while its linear response to ionization predicts changes in bonding patterns. The derivative of the shape entropy proposed turned out to be fully determined by the shape function and the Fukui function.
RESUMO
The computational limits of accurate electron propagator methods for the calculation of electron binding energies of large molecules are usually determined by the rank of the virtual orbital space. Electron density difference matrices that correspond to these transition energies in the second-order quasiparticle approximation may be used to obtain a virtual orbital space of reduced rank that introduces only minor deviations with respect to the results produced with the full, original set of virtual orbitals. Numerical tests show the superior accuracy and efficiency of this approach compared to the usual practice of omission of virtual orbitals with the highest energies.
