CALCULATION OF ADSORPTION ENERGIES OF MOLECULES IN CAGES - A DENSITY-FUNCTIONAL APPROACH

A density functional theory (DFT)-based method for the calculation of interaction energies in adsorption processes is proposed. The expressi on is based on the expansion of the energy of the adsorbed molecule wi th respect to the external potential perturbation introduced by adsorp tion in the zeolite cage. DFT interaction energies at the B3LYP/G-31G level for the N-2... Na+, Na+... CO and CO ... Na+ systems in the gas phase were compared with first- and second-order results, resulting f rom the DFT expansion of the interaction energy. The distance dependen ce of the second-order contribution was investigated. The present meth od was shown to be an interesting computational strategy for calculati ng interaction energies when evaluating Henry constants. (C) 1998 Else vier Science B.V. All rights reserved.