Combinative energy between two structural blocks and superconductivity in LaFe1−xCoxAsO

► A relationship between the combinative energy and Tc is found in LaFe1−xCoxAsO system and even LnOFeAsF systems. ► Our calculation indicates an itinerant electron character in LaFe1−xCoxAsO system. ► The relationship can be well explained with the charge-transfer model and matches the “misfit strain” supposition very well.