collapse

Maybe it is a PC related problem, but
when I try to annulate rings simply by moving the mouse to enlarge or diminish
the second ring, the program collapses. (If I build the rings atom-wise there
is no problem, but the process is much slower). The other phenomenon: when I
try to calculate the partial charges of some atoms, the same collapse occurs.
Has somebody else experienced the same problem? What may be the reason?