Conversion of Cohesive energy density (J/m3 to J/m2)

Hi all,

In the following paper:
Surface Energy and the Contact of Elastic Solids, Author(s): K. L. Johnson, K. Kendall and A. D. Roberts, Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, Vol. 324, No. 1558 (Sep. 8, 1971), pp. 301-313

The cohesive energy density is mentioned in J/m2 but in LIGGGHTS we have to use the same in J/m3. So, can anyone elaborate the conversion method for cohesive energy density.