cell opt calculation, default pressure value

[Conrad]

Hi Davide,

I think the short answer is that the pressure is very sensitive to the lattice parameters. Try for 1 bar if you wish, but you may find it tricky to converge for your system. 

Have a quick look on a mineralogy database. You'll see that the difference in lattice parameters for solid crystals is maybe only 0.1 angstrom between 1 bar and 100 kilobar.

Thanks, 
Conrad