Conditionally inserts an atom of type <name> at the position <x,y,z> in crystal space. The temperature coefficient must be given. 'appe' checks the position <x>,<y>,<z> with respect to all atoms numbered <na> to <ne>. The new atom is NOT inserted, if any of these atoms is within the block <x> +- <delx>; <y> +- <dely>; <z> +- <delz>. If <dely> and/or <delz> are not given, then they default to the value of the last <del.> given on this 'appe' command.
Note, that the <del.> are in fractional coordinates, NOT in Angstroem.
In the alternative form, the eight's parameter is interpreted as a bond distance. To distinguish the two forms, the bondlength must be less than zero. The new atom is inserted, if no atom is less than <bondlength> Angstroem from the position <x>,<y>,<z>.
If the crystal is empty, i.e. n[1]=0, the 'append' command ignores the parameters <na>,<ne>, <delx> [,<dely> [,<delz>]]. Since there is no atom within the crystal, there is no need for a comparison. Effectively, the 'append' command acts just as an equivalent 'insert' command.