Cohesive Energy of Diamond

Abstract

The cohesive energy of diamond crystal has been calculated by the use of the SLCO (Semi-Localized Crystalline Orbital) method developed by Morita in 1958. One method of the orthogonalization of the crystalline orbitals is presented and performed in detail. The cohesive energy is calculated to be −0.24 a.u./atom, which is in good agreement with the observed value, −0.273 a.u./atom. It is pointed out that a configuration mixing of the anti-bonding orbitals to the bonding orbitals is an important factor in stabilizing the crystalline state. It is also noted that the neglect of the effect of the nonorthgonality of orbitals results in an unreasonable value +0.44 a.u./atom for the cohesive energy.