Molecular approach to hexagonal and cubic diamond nanocrystals

In the present work, we propose a molecule (C14H14) that can be used as a building block of hexagonal diamond-type crystals and nanocrystals, including wurtzite structures. This molecule and its combined blocks are similar to diamondoid molecules that are used as building blocks of cubic diamond crystals and nanocrystals. The hexagonal part of this molecule is included in the C-12 central part of this molecule. This part can be repeated to increase the ratio of hexagonal to cubic diamond and other structures. The calculated energy gap of these molecules (called hereafter wurtzoids) shows the expected trend of gaps that are less than that of cubic diamondoid structures. The calculated binding energy per atom shows that wurtzoids are tighter structures than diamondoids. Distribution of angles and bonds manifest the main differences between hexagonal and cubic diamond-type structures. Charge transfer, infrared, nuclear magnetic resonance and ultraviolet-visible spectra are investigated to identify the main spectroscopic differences between hexagonal and cubic structures at the molecular and nanoscale. Natural bond orbital population analysis shows that the bonding of the present wurtzoids and diamondoids differs from ideal sp(3) bonding. The bonding for carbon valence orbitals is in the range (2s(0.98)2p(3.21)3p(0.02))-(2s(0.94)2p(3.31)3p(0.02)) for wurtzoid and (2s(0.93)2p(3.29)3p(0.01))-(2s(0.99)2p(3.44)3p(0.01)) for diamantane.