code: public Chain getCurrentChain(){
  		if ( current_model_pos >= structure.nrModels()){
  			return null;
  		}
  
  		List<Chain> model =  structure.getModel(current_model_pos);
  
  		if ( current_chain_pos >= model.size() ){
  			return null;
  		}
  
  		return model.get(current_chain_pos);
  
  	}
docs: Get the current Chain. Returns null if we are at the end of the iteration.
  
  @return the Chain of the current position