I was developing code to allow pasting of cartesian coordinates but noticed if i pasted two of the same coordinates and then tried to optimize there becomes an error. Here is a sample .gpr file that can be used to reproduce the error. Even though it's not practical it should be considered an error. Before I add the duplicate atom coordinate "check" i wanted to make sure we couldn't fix this problem in the libghemical tools. !Header gpr 111 !Info 1 allmm 80 !Atoms 2 0 6 0 0 1 6 0 0 !Bonds 0 !Coord 0 +0.146979093551636 -0.0122482553124428 +0 1 +0.146979093551636 -0.0122482553124428 +0 !PartialCharges 0 +0 1 +0 !End -------------- next part -------------- !Header gpr 111 !Info 1 allmm 80 !Atoms 2 0 6 0 0 1 6 0 0 !Bonds 0 !Coord 0 +0.146979093551636 -0.0122482553124428 +0 1 +0.146979093551636 -0.0122482553124428 +0 !PartialCharges 0 +0 1 +0 !GAMESS !End