This indicates that unpaired electrons of the system do not change during the catalytic cycle reactions. The criteria of convergence such as gradients of root-mean-square (rms) displacement, max displacement, rms force and max force in a calculation are 12 × 10−4, 18 × 10−4, 3 × 10−4 and 45 × 10−5, respectively. Although dispersion interactions might play an important role, it has not been taken into account in the present study since screening of activity for hydrogen sulfide (H2S) adsorption on metal atoms in ZSM-12 zeolite has been examined. This effect would likely be similar for each of these cluster systems