You can
simulate the tunneling spectrum of the scanning tunneling spectroscopy (STS).
You can examine physical properties of thin layers made of metals and semiconductors which through which the tunneling current passes.
You can even examine physical properties of a sample material of organic compounds, if the tunneling current passes through it.
The DFTB solver can simulate compounds consisting of the following 69 kinds of elements at a maximum, so that you can simulate almost all organic and non-organic compounds as sample materials actually:
H, Li, Be, B, C, N, O, F, Na, Mg, Al, Si, P, S, Cl, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, I, Cs, La, Ce, Ba, Gd, Tb, Dy, Ho, Er, Tm, Yb, W, Re, Ir, Pt, Au, Hg, Pb, Bi, U