Density Functional Theory (DFT) and Quasi Harmonic Approximation (QHA) on Isotope effect of Methane Absorbed on Ag(111) Surface

Abstract

<div class="textLayer"><span dir="ltr">We investigated the isotope effect of methane (CH4) on Ag(111) using van der Waals density </span><span dir="ltr">functional and the quasi-harmonic approximation.</span><span dir="ltr">In this study, we combined two methods to </span><span dir="ltr">investigate the nuclear quantum effect in methane adsorption on an Ag(111) surface. We obtained </span><span dir="ltr">that the adsorption potential energies of CD</span><span dir="ltr">4</span><span dir="ltr">on fcc Ag(111) surfaces are shallower than those </span><span dir="ltr">of CH</span><span dir="ltr">4</span><span dir="ltr">, whereas the equilibrium distances from the surface are larger.</span><span dir="ltr">The similiar finding also </span><span dir="ltr">observed in our previous study, however, Ag(111) gives smaller energies.</span><span dir="ltr">It is found that the </span><span dir="ltr">similar softening of the C-H bond pointing toward the surface is the cause of the isotope effect. </span><span dir="ltr">This softening leading to lowering the vibrational frequency and large zero-point energy difference </span><span dir="ltr">between CH</span><span dir="ltr">4</span><span dir="ltr">and CD</span><span dir="ltr">4</span><span dir="ltr">.</span><br /><br /></div><div class="annotationLayer"> </div>