Path integral molecular dynamics for hydrogen adsorption site of zeolite-templated carbon with semi-empirical PM3 potential

Abstract

To evaluate the adsorption sites of hydrogen atom on buckybowl-like molecule (C 36H 12), which is a model fragment structure of zeolite-templated carbon (ZTC), we have performed path integral molecular dynamics (PIMD) simulation including thermal and nuclear quantum fluctuations under the semi-empirical PM3 potential. Here we have picked up ten carbons as the adsorption sites of additional hydrogen atom (H *), which are labeled as α-, β 1-, β 2-, γ-, and δ-carbon from edge to bottom carbon for inside and outside of C 36H 12, respectively. In the static PM3 calculation and conventional MD simulation the ten stable adsorption sites of H * are obtained both inside and outside of C 36H 12. In PIMD simulation, on the other hand, the nine stable adsorption sites are obtained, except for δ-carbon for inside of C 36H 12. This result is due to the fact that the thermal effect and zero point vibration of δ-carbon and H * stretching motion make adsorbed hydrogen atom go over potential barrier from δ- and β 1-carbon for inside of C 36H 12 more readily. The thermal and nuclear quantum effects are important to evaluate the hydrogen adsorption site on carbon materials.