  Motivated by the recent discovery of Dirac nodal line in the single-component
molecular conductor [Pt(dmdt)$_{2}$], we propose a three-orbital tight-binding
model based on the Wannier fitting of the first-principles calculation, and
address the problems of edge states, topological properties and magnetic
susceptibility. We find that logarithmic peaks of the local density of states
emerge near the Fermi energy, owing to pseudo-one-dimensional edge states that
appear between the Dirac nodal lines. Magnetic susceptibility calculated in our
model can explain the experimental result at a high temperature. In the
presence of a realistic spin-orbit coupling, we show that [Pt(dmdt)$_{2}$] is a
topological nodal line semimetal with isolated electron and hole pockets.
