goto CHARMM:;
print "running charmm for iteration $iter with command: ~u0588832/bin/charmm < enm.calc.inp > charmm-out-iter-$iter.out\n";
system ("~u0588832/bin/c32b2/exec/gnu/charmm < enm.calc.inp > charmm-out-iter-$iter.out");

if ($? == -1) {
                print "failed to execute: $!\n";
        }
        elsif ($? & 127) {
                printf "child died with signal %d, %s coredump\n",
                ($? & 127),  ($? & 128) ? 'with' : 'without';
        }
        else {
                printf "child exited with value %d\n", $? >> 8;
        }


rename ("ic-fluc.dat" , "ic-fluc-iter-$iter.dat");
open(IN, "ic-fluc-iter-$iter.dat") || die "could not open internal coord fluc file.\n";