Z1, Z2

These are the two forms of the Zetterling potential:[53]

$$V(r)=a {e^{\alpha r}\over r^3} \cos(2k_F r)+b\left({\sigma\over r}\right)^{n}+V_0.$$ (1)

Subroutines used: Z1 and Z2 etc. If three parameters are specified by the PARAMS keyword they are interpreted as box lengths for a periodic system.