the question about script in VNL tutorial

[fanjiaping]

   In the part of Custom builder for the Li-H2-Li device system, there are some codes list as "builder.double('distance_h_h'  , 0.804, 'H/H  distance (Ang)' , min=0.01, max=1000)"
the queation I want to ask is why we set the min equal to 0.01? can we change it to others value,such as 0.02?

[Anders Blom]

Sure. The minimum is just the smallest value you can enter in this box, you can set it to anything you want. There is also a "max".

Why 0.01? Well, it hardly makes any sense to set the H-H distance smaller, but if the minimum is zero then you can set it to zero, which makes the atoms end up on top of each other, and this is bad. Of course, 0.01 will not really work in practice either, so you can argue maybe a better minimum is 0.1 Å, or maybe 0.2, or maybe 0.5. Or something else. In the end, we just need a minimum, it's up to the user to choose a suitable value. So, the 0.01 is just a small number, and it prevents you from setting the distance to exactly zero.