▁This ▁is ▁only ▁known ▁to ▁occur ▁when ▁there ▁are ▁at ▁least ▁ 3 ▁i od ine ▁atoms ▁attached ▁to ▁an ▁ ▁cluster , ▁. ▁The ▁an ionic ▁cluster ▁has ▁a ▁total ▁of ▁ 4 3 ▁it iner ant ▁electrons , ▁but ▁the ▁three ▁i od ine ▁atoms ▁each ▁remove ▁one ▁of ▁the ▁it iner ant ▁electrons ▁to ▁leave ▁ 4 0 ▁electrons ▁in ▁the ▁j elli um ▁shell . ▁ ▁It ▁is ▁particularly ▁easy ▁and ▁reliable ▁to ▁study ▁atomic ▁clusters ▁of ▁in ert ▁gas ▁atoms ▁by ▁computer ▁simulation ▁because ▁interaction ▁between ▁two ▁atoms ▁can ▁be ▁approxim ated ▁very ▁well ▁by ▁the ▁L enn ard - J ones ▁potential . ▁Other ▁methods ▁are ▁readily ▁available ▁and ▁it ▁has ▁been ▁established ▁that ▁the ▁magic ▁numbers ▁are ▁ 1 3 , ▁ 1 9 , ▁ 2 3 , ▁ 2 6 , ▁ 2 9 , ▁ 3 2 , ▁ 3 4 , ▁ 4 3 , ▁ 4 6 , ▁ 4 9 , ▁ 5 5 , ▁etc . ▁▁▁ ▁= ▁the ▁property ▁is ▁similar ▁to ▁g erman ium ▁atoms . ▁▁ ▁= ▁the ▁property ▁is ▁similar ▁to ▁hal ogen ▁atoms , ▁more ▁specifically , ▁ch lor ine . ▁ ▁, ▁where ▁. ▁▁ ▁= ▁the ▁property ▁is ▁similar ▁to ▁al kal ine ▁earth ▁met als . ▁ ▁, ▁where ▁. ▁ ▁Other ▁clusters ▁ ▁Li ( H F ) 3 Li ▁= ▁the ▁( H F ) 3 ▁interior ▁causes ▁ 2 ▁val ence ▁electrons ▁from ▁the ▁Li ▁to ▁orbit ▁the