UT theoretical chemistry code forum

hello:
I'm a new user from china, now I come across a problem. When I input the order
chgsum.pl AECCAR0 AECCAR2
it say: chgsum.pl: command not found
I chmod the chgsum.pl before input the order.
I download the chgsum.pl script from this website.
who can tell me why!
thanks!
PS:forgive my poor ...