Hi John, The only better way would be to use non-periodic-boundary conditions. 15 Angs is already good enough to have the molecule essentially isolated. Since you're dealing with a non-periodic system, Gamma point sampling is good enough provided that the enclosing box is big enough - your case. However, beware that to calculate the adsorption energy you'll have to use BSSE corrections.
Marcos Vous avez écrit / You have written / Lei ha scritto / Você escreveu... John Appleton > Hello, > > I wish to adsorb O2 (oxygen molecule) on a metal surface. > To compute the energy of the isolated (free) molecule, I > used a cubic box of length 15 Ang and the Gamma k-point. > Is the approach correct or there is a better way? > -- Dr. Marcos Verissimo Alves Post-Doctoral Fellow Unité de Physico-Chimie et de Physique des Matériaux (PCPM) Université Catholique de Louvain 1 Place Croix du Sud, B-1348 Louvain-la-Neuve Belgique ------ I have become so addicted to vi that I try to exit OpenOffice by typing :wq!
