Firstly, call "nlPrint(your configuration)" to print out the atomic coordinates of your configuration; and then collect it and make a file with XYZ format. Finally, visualize this xyz file with "JMOL" software (free), in this software, the id numbers of atoms (one thing should be pointed out, the id numbers in JMOL start from 1 rather than 0. In ATK, the id number starts from 0.) can be easily obtained by selecting "Display--->Label--->Name".