code: private List<String> getChainIds(Structure asymUnit) {
  		List<String> chainIds = new ArrayList<String>();
  		for ( Chain c : asymUnit.getChains()){
  			String intChainID = c.getId();
  			chainIds.add(intChainID);
  		}
  		return chainIds;
  	}
docs: Returns a list of chain ids in the order they are specified in the ATOM
  records in the asymmetric unit
  @param asymUnit
  @return