  Diamondoids and their derivatives have found major applications as templates
and as molecular building blocks in nanotechnology. Applying ab initio method,
we calculated the quantum conductance and the essential electronic properties
of two lower diamondoids (adamantane and diamantane) and three of their
important derivatives (amantadine, memantine and rimantadine). We also studies
two artificial molecules that are built by substituting one hydrogen ion with
one sodium ion in both adamantane and diamantane molecules. Most of our results
are based on an infinite Au two-probe system constructed by ATK and VNL
software, which comprise TRANSTA-C package. By changing various system
structures and molecule orientations in linear Au and 2 by 2 Au probe systems,
we found that although the conductance of adamantane and diamantane are very
small, the derivatives of the lower diamondoids have considerable conductance
at specific orientations and also showed interesting electronic properties. The
quantum conductance of such molecules will change significantly by changing the
orientations of the molecules, which approves that residues like nitrogen and
sodium atoms have great effects on the conductance and electronic properties of
single molecule. There are obvious peaks near Fermi energy in the transmission
spectrums of artificial molecules, indicating the plateaus in I-V
characteristics of such molecules.
